The  Petrography  and  Genesis  of 

the  Sediments  of  the  Upper 

Cretaceous  of  Maryland 


THE  LIBRARY 

OF 

THE  UNIVERSITY 
OF  CALIFORNIA 

LOS  ANGELES 


The  RALPH 

DEP 

UNIVi: 

iUK. 


THE  PETROGRAPHY  AND  GENESIS 

OF  THE  SEDIMENTS  OF  THE  UPPER 

CRETACEOUS  OF  MARYLAND 


A  DISSERTATION 

Submitted  to  the  Board  of  University  Studies  of  The  Johns  Hopkins  University 

in  conformity  with  the  requirements  for  the  degree  of 

Doctor  of  Philosophy 


BY 

MARCUS  I.  GOLDMAN 

June  1913 


BALTIMORE 
THE  JOHNS  HOPKINS  PRESS 

1916 


THE  PETROGRAPHY  AND  GENESIS 

OF  THE  SEDIMENTS  OF  THE  UPPER 

CRETACEOUS  OF  MARYLAND 


A  DISSERTATION 

Submitted  to  the  Board  of  University  Studies  of  The  Johns  Hopkins  University 

in  conformity  with  the  requirements  for  the  degree  of 

Doctor  of  Philosophy 


BY 

MARCUS  I.  GOLDMAN 

June  r9ij 


BALTIMORE 
THE  JOHNS  HOPKINS  PRESS 

1916 


Geology 
Library 


471 


THE  PETROGRAPHY  AND  GENESIS  OF  THE 

SEDIMENTS  OF  THE  UPPER  CRETACEOUS 

OF  MARYLAND 

BY 

MARCUS  I.  GOLDMAN 


INTRODUCTORY 

The  object  of  this  chapter  is  to  present  the  results  of  the  detailed  study 
and  the  mechanical  and  microscopical  analysis  of  a  few  typical  sediments 
from  the  Upper  Cretaceous  of  Maryland.  Work  of  this  kind  is  merely 
an  extension  of  petrography  to  the  sedimentary  rocks ;  yet  it  has  hitherto 
been  so  little  practised  that  most  geologists  hearing  the  term  petrography 
think  instinctively  of  crystalline  rocks.  This  comment  is  made  in  order 
to  forestall  an  attitude  of  mind  towards  what  follows  that  is  very  gen- 
eral, namely  the  belief  that  after  such  an  analysis  of  a  sedimentary  rock 
it  is  possible  to  determine  the  conditions  under  which  the  rock  originated. 
That  is,  of  course,  the  ultimate  object  of  such  work,  yet  it  is  no  more 
implicitly  the  immediate  result  of  the  study  of  a  given  rock  than  the 
study  of  a  given  crystalline  rock  in  the  beginning  of  that  science  was  the 
direct  key  to  the  origin  of  the  rock — or  is  to-day,  for  that  matter.  If 
decades  of  study  of  conglomerates,  whose  composition  is  apparent  to  the 
unaided  eye,  leave  many  fundamental  problems  concerning  this  rela- 
tively simple  type  of  rock  still  unsolved,  it  is  not  to  be  expected  that 
microscopic  knowledge  of  facts  of  the  same  kind  about  the  sedimentary 
rocks  of  finer  grain  will  suddenly  reveal  the  conditions  of  their  origin. 
In  fact,  for  these  finer-grained  rocks,  as  for  the  conglomerates,  field  study 
of  their  larger  geological  characters,  thair  variations  vertically  and  hori- 
zontally, the  form  of  the  whole  mass,  its  relations  to  adjacent  beds,  and 
other  features  must  remain  as  important  as  the  laboratory  analysis.  But 
a  more  detailed  knowledge  of  the  composition  of  the  finer-grained  sedi- 


112  THE  PETROGRAPHY  AND  GENESIS  OF  SEDIMENTS 

mentary  rocks  is  desirable  than  the  current  terms,  sandstone,  shale,  sandy 
shale,  tuff,  limestone,  or  even  more  circumscribed  terms  like  chalk,  green- 
sand,  etc.,  afford;  and  from  the  awakening  interest  in  this  subject  it  is 
safe  to  expect  that  before  long  every  stratigraphic  study  of  a  limited 
region  will  contain  descriptions  of  the  composition  of  the  sedimentary 
rocks  involved.  Every  such  study  will  bring  out  some  significant  facts 
regarding  the  origin  of  the  particular  rocks,  but  for  a  satisfactory  final 
interpretation  of  the  conditions  under  which  the  rock  originated  it  will  be 
necessary  to  have  accumulated  an  extensive  series  of  analyses  of  modern 
sediments  of  all  possible  varieties.  Comparing  then  the  ancient  sediment 
with  the  modern  ones,  the  conditions  of  whose  origin  will  be  more  or  less 
completely  known,  it  will  be  possible  by  finding  the  modern  sediment  that 
is  most  similar  to  determine  the  conditions  under  which  the  ancient  sedi- 
ment in  question  was  formed.  On  the  other  hand,  the  sediments  of  the 
past  offer  some  opportunities  to  the  investigator  that  are  lacking  in  the 
modern.  For  in  the  subaqueous  sediments  of  to-day  only  what  is  at  the 
surface,  or  a  few  feet  below,  can  be  examined.  Of  the  ancient  sediments, 
however,  it  is  possible  to  obtain  sections  in  which  the  changes  both  vertical 
and  lateral  can  be  followed  out,  and  thus  knowledge  gained  which  could 
be  gathered  from  sediments  in  process  of  formation  only  through  cen- 
turies of  observation  or  through  periods  too  long  for  consideration.  Thus 
the  two  branches  of  the  study  must  advance  together,  each  throwing  light 
on  the  facts  of  the  other,  and  the  two  pointing  out  to  each  other  the 
problems  that  require  special  attention. 

It  is  this  consideration  that  has  led  to  the  attempt  to  interpret  freely 
the  facts  obtained  in  the  present  study  in  the  belief  that  an  investigation 
is  valueless  until  some  conclusion  has  been  drawn  from  it,  and  that  the 
investigator  who  has  accumulated  the  facts  is  in  the  most  advantageous 
position  for  interpreting  them.  These  interpretations,  however,  are  put 
forward  most  tentatively  and  with  the  greatest  possible  reservation. 

While  the  published  literature  describing  modern  sediments  is  not 
inconsiderable,1  it  is  not  of  much  value  for  the  Cretaceous  sediments 

1  For  a  very  full  and  up-to-date  bibliography,  see  Andrge,  K.,  Ueber  Sediment- 
bildung  am  Meeresboden  Geol.  Rundschau,  vol.  3,  1912,  H  5/6,  pp.  324-338. 


MARYLAND  GEOLOGICAL  SURVEY  113 

because  most  of  it  deals  with  the  deposits  of  the  deeper  ocean,  little  with 
the  deposits  near  and  adjacent  to  the  mouths  of  rivers.  Probably  no  inves- 
tigator of  modern  sediments  has  had  the  geologic  bearings  of  the  study  so 
forward  in  his  mind  as  Thoulet,  and  it  is  his  publications  therefore,  limited 
in  extent  though  the  work  of  one  man  must  be,  that  are  of  most  value 
to  the  geologist.  Foremost  in  his  work  in  this  connection  stands  the 
recently  published  monograph,  with  colored  maps,  of  the  sediments  of 
the  Gulf  of  Lyon ;  *  and  the  work  of  his  pupil  Sudry 2  on  the  Lagoon  of 
Thau  in  the  same  region  is,  as  subsequently  pointed  out,  probably  of  par- 
ticular bearing  on  the  Matawan.  (See  especially  sample  8,  below.) 

Eeferences  to  such  studies  as  have  been  made  of  near-shore  sediments 
will  be  found  in  Andree's  bibliography,  but  as  far  as  I  know  the  only  syste- 
matic and  continuous  investigation  of  this  type,  and  the  only  one  whose 
results  are  expressed  in  the  tangible  form  of  a  map  is  that  by  Thoulet  of 
the  Gulf  of  Lyon.  In  fact  it  is,  I  believe,  the  need  for  studies  of  this 
kind  that  inspired  him  to  carry  out  the  work. 

THE  METHOD  OF  ANALYSIS 

In  all  essentials  it  is  Thoulet's  3  method  of  analysis  that  has  been  fol- 
lowed in  this  investigation. 

In  a  general  way  three  main  types  of  procedure  in  the  analysis  of  unin- 
durated  sediments,  whether  ancient  or  modern,  may  be  recognized.  The 
first  is  the  method  of  elutriation  in  which  a  separation,  mainly  of  the  clay 
and  finer  parts  from  the  sand,  is  made  by  subjecting  the  sample  to  a  rising 
current  of  water  whose  velocity  is  known  and  can  be  regulated.  This 
method  cannot  be  used,  however,  to  subdivide  material  finer  than  ^  mm., 
because  finer  particles  settle  too  slowly  to  oppose  any  velocity  of  current 

1  Thoulet,  J.,  Etude  bathylithologique  des  cotes  du  Golfe  du  Lion.    Annales 
de  1'Inst.  Oc6anograph.,  T.  iv,  Fasc.  6,  Paris,  1912,  66  pp.     Maps. 

2  Sudry,  L.,  L'Etang  de  Thau.  Ann.  de  I'Inst.  Oc6anograph.,  T.  i,  Fasc.  10, 
Monaco,  1910,  208  pp. 

3  Thoulet,  J.,  Pr6cis  d'analyse  des  fonds  sous-marins  actuels  et  anciens.  Paris: 

Chapelot  et  Cie,  1907,  220  pp. Instructions  pratiques  pour  l'6tablissement 

d'une  carte  bathymetrique-lithologique  sous-marine.     Bull,   de  I'Inst.   Oc6an- 
ograph.,  No.  169,  Monaco,  1910,  29  pp. 


114  THE  PETROGRAPHY  AND  GENESIS  OF  SEDIMENTS 

that  is  practically  attainable.  Theoretically  there  would  seem,  however, 
possibilities  of  its  unlimited  extension  to  finer  sizes  in  the  centrifugal 
elutriator  of  Yoder,1  in  which  the  velocity  that  the  particles  oppose  to  the 
current  is  greatly  increased  by  centrifugal  force. 

The  second  method,  developed  by  Mitscherlich,2  determines  the  rela- 
tive internal  surface  of  a  soil.  There  are  two  distinct  procedures  for 
arriving  at  this  quantity.  The  first  is  based  on  the  fact  that  when  water 
is  brought  into  contact  with  a  perfectly  dry  porous  or  powdered  substance 
a  certain  heat  is  developed  which  is  a  function  of  the  internal  surface  of 
the  substance.  The  finer  its  particles  the  greater,  of  course,  will  this 
surface  be,  and  the  greater,  therefore,  the  heat  developed.  In  practice  it 
is  more  convenient  to  adopt  the  second  procedure,  which  determines  the 
hygroscopicity  of  the  substance,  that  is,  the  amount  of  water  which  the 
material  will  take  up  out  of  a  saturated  atmosphere.  This  quantity,  as 
explained  by  Mitscherlich,  is  also  supposed  to  have  a  definite  relation  to 
the  internal  surface.8 

The  third  method,  and  the  one  most  generally  employed,  is  that  of 
sieving  the  sands  in  conjunction  with  washing  out  the  mud.  It  is  to  this 
group  that  the  method  of  Thoulet  belongs,  as  well  as  that  of  Murray,  the 
U.  S.  Department  of  Agriculture,  and  others.  To  these  methods  are 
added  certain  accessory  procedures  (the  essential  part  of  some  less  gen- 
erally practised  methods)  such  as  treatment  in  heavy  liquid,  by  the  electro- 
magnet, with  acids,  etc. 

There  is  no  room  for  lengthy  discussion  of  the  relative  values  of  these 
three  methods;  but  for  the  purpose  in  hand  the  method  by  elutriation  is 
theoretically  and  practically  the  most  satisfactory,4  since  it  classifies  the 

1  Yoder,  P.  A.,  Bull.  No.  89,  Utah  Exper.  Sta.,  1904. 

2  Mitscherlich,  E.  A.,  Bodenkunde,  Berlin,  1905,  pp.  49-70. 

3  An  attempt  to  eliminate  the  effect  of  the  internal  surface  of  the  particles 
(that  is  minute  fissures  or  pores  in  them)  has  been  made  by  Franz  Scheefer: 
Eine  Methode  zur  Bestimmung  der  ausseren  Bodenoberflache.  Dissert.  Konigs- 
berg.  i.  Pr.,  1909. 

4  Thoulet,  Precis  d'analyse  (op.  clt),  65-67. Hilgard,  E.  W.,  Soils.  1906, 

pp.  90-93. Ries,  H.,  Clays.  1906,  pp.  113-115. Andrge,  K.,  Ueber  Sediment- 

bildung  am  Meeresboden  (op.  cit. ),  pp.  350,  351. 


MARYLAND  GEOLOGICAL  SURVEY  115 

sediments  by  the  relative  settling  velocities  of  their  constituents,  which  is 
the  significant  factor  in  sedimentation,  and,  on  account  of  the  time  allowed 
for  working  over  the  material  in  the  elutriator,  tends  to  classify  them  very 
successfully.  Its  defect  is  the  great  amount  of  distilled  water,  time,  and 
attention  it  requires.  The  method  of  determining  surface  by  heat  of 
moistening  or  hygroscopicity  seems  to  have  the  defect  that  it  gives  only  a 
single  value  for  each  sample,  so  that  sediments  made  up  of  very  different 
proportions  of  the  various  sizes  might  yet  give  the  same  results.  It  is 
really  a  method  that  has  much  more  significance  for  soils,  for  which  it  was 
devised,  than  for  sediments  to  which  it  has,  however,  been  very  recently 
applied.1 

The  method  here  followed,  which  is  that  of  Thoulet  with  some  modifi- 
cations as  will  be  noted,  is  essentially  as  follows:  A  large  portion  of  the 
sample  is  first  passed  through  sieves  with  respectively  3,  6,  and  10  meshes 
to  the  inch,  and  the  portion  retained  is  classed  as  gravel,  though  con- 
cretions of  these  sizes  should  of  course  be  separately  considered.  As  a 
matter  of  fact,  none  of  the  samples  contained  any  gravel  that  would  not 
pass  the  3-mesh  sieve;  very  few,  indeed,  any  gravel  at  all,  and  then  only 
very  little.  As  the  material  was  dried  at  105°  it  was  necessary  to  know  the 
proportion  of  gravel  in  such  dried  material,  but  it  would  not  have  been 
pratical  to  dry  the  large  portion  required  for  gravel  determination.  The 
whole  lot  was  therefore  weighed  merely  air-dried,  and  at  the  same  time 
a  small  portion  weighed  separately,  dried  for  about  eight  hours  at  105°  C., 
and  the  percentage  loss  in  drying  determined.  This  loss  was  then  applied 
to  the  large  lot  in  which  the  gravel  had  been  determined.  For  the  rest 
of  the  analysis  about  10  gm.  of  the  sample,  if  necessary  crushed  some- 
what in  order  to  facilitate  drying,  is  dried  for  about  eight  hours  at  a 
temperature  maintained  as  nearly  as  possible  at  105°.  The  sample  was 
cooled  in  a  dessicator  and  weighed  rapidly;  but  the  avidity  with  which 
the  dried  samples  took  up  moisture  gave  an  accuracy  of  not  more  than 
5  mg.  to  10  mg.  The  balance,  moreover,  that  was  used  for  the  later 

1  Kiippers,  E.,  Physlkalische  u.  mineralogisch-geologische  Untersuchung  von 
Bodenproben  aus  Ost-  u.  Nordsee.  Wiss.  Meeresuntersuch.  Herausgegeb.  v.  d. 
Kommiss.  z.  Untersuch.  d.  deutsch.  Meere,  etc.,  1908,  N.  F.,  vol.  x,  pp.  1-11. 


116  THE  PETROGRAPHY  AND  GENESIS  OP  SEDIMENTS 

analyses  did  not  have  a  reliable  accuracy  of  more  than  5  mg.,  which  is 
the  smallest  unit  to  which  weights  were  then  recorded.  The  sample  was 
next  washed  into  an  8  oz.  milk-sterilizing  bottle  with  water  and  generally 
a  little  ammonia  to  help  disintegrate  the  clay.  The  bottle  was  then  shaken 
on  a  rotary  shaker.  This  is  simply  an  axis  to  which  a  board  is  fastened. 
The  bottle  is  attached  to  the  board  at  right  angles  to  the  axis  with  the 
middle  of  the  bottle  over  the  axis,  so  that  when  the  axis  is  rotated  the 
sediment  and  water,  which  should  less  than  half  fill  the  bottle,  flop  from 
one  end  of  the  bottle  to  the  other  twice  in  one  revolution  and  by  this 
jarring  the  sample  disintegrates.  The  method  seemed  fairly  effective; 
just  how  effective  it  is  hard  to  say.  Certainly  in  some  of  the  samples 
there  was  a  perceptible  amount  of  clay  granules,  a  little  in  all;  they  are 
mentioned  in  some  of  the  analyses  that  follow,  though  they  are  not  con- 
sistently recorded.  But  it  is  a  question  whether,  in  some  cases  at  least, 
these  clay  granules  are  not  an  essential  part  of  the  sediment  representing 
some  kind  of  growth  or  concretion  in  the  clay.  That  there  is  a  possibility 
of  the  existence  of  such  concretions  is  indicated  by  the  round,  clay-like 
granules  with  faint  aggregate  polarization  that  were  found  in  a  few  of 
the  samples  (see  sample  4)  and  believed  to  represent  a  stage  intermediate 
between  clay  and  glauconite.  The  uncertainty  prevailing  in  the  whole 
matter  appears  from  the  difference  of  opinion  concerning  the  best  method 
of  disintegrating  clay,  Mitscherlich,  e.  g.,  recommending  that  the  sample 
be  boiled  some  fifteen  minutes,  while  others  say  that  only  hike-warm 
water  should  be  used,  because  hot  water  coagulates  the  clays. 

After  being  shaken  ten  to  thirty  hours,  according  to  the  apparent 
amount  of  clay  in  the  sample,  the  material  is  washed  out  of  the  bottle  into 
an  evaporating  dish  of  12  cm.  diameter.  Here  it  is  allowed  to  settle  for  a 
while,  the  mud  decanted  into  a  1500  c.  c.  separating  funnel,  hot  wash 
water  added  in  the  evaporating  dish,  the  settling  and  decantation  repeated, 
etc.,  several  times.  The  length  of  time  during  which  the  material  was 
allowed  to  settle  varied  for  different  samples  and  decreased  for  each  suc- 
cessive decantaion.  If  the  sample  was  muddy  the  writer  started  with 
fifteen  minutes,  allowed  ten  minutes  on  the  second  settling  and  so  on  down, 
depending  somewhat  on  the  observed  rate  of  clearing  of  the  upper  part  of 


MARYLAND  GEOLOGICAL  SURVEY  11? 

the  suspension.  This  appears  to  have  been  more  time  than  Thoulet 
allowed,  but  it  was  probably  on  this  account  that  very  little  residue  from 
the  material  tapped  from  the  separating  funnel  was  obtained.  Another 
slight  adaptation  of  Thoulet's  method  consisted  in  fixing  the  time  for  the 
last  settling  at  thirty  seconds.  That  is,  all  the  "  sand  "  and  "  silt  "  had  to 
settle  in  that  time.  This  period  was  chosen  on  the  basis  of  practical 
experience  with  the  samples,  which  showed  that  the  interval  was  sufficient 
to  allow  all  but  a  certain  cloudiness  to  settle  out.  In  many  samples,  how- 
ever, it  was  found  that  there  was  a  sort  of  transition  material  which  not 
only  had  a  different  appearance  from  the  sand  but  also  did  not  seem  to 
settle  with  the  same  promptness  as  the  sand,  forming  a  sort  of  interme- 
diate constituent.  Microscopic  examination  justified  this  conclusion  as, 
according  to  the  constitution  of  the  sample,  ^regular  glauconitic  frag- 
ments', limonitic  fragments,  or  small  clay  flakes  secondarily  cemented 
appeared  in  this  intermediate  product.  The  determination  of  the  amount 
of  this  product  settling  in  thirty  seconds  but  not  in  ten,  was  most 
unsatisfactory,  since  the  quantity  depended  largely  on  the  amount  of 
water  in  the  evaporating  dish,  the  temperature  of  the  water  as  affecting 
convection  currents,  and  probably  other  factors,  so  that  it  was  possible 
to  wash  back  much  of  the  material  that  had  once  been  washed  out,  and 
vice  versa,  by  continuing  washing  to  keep  on  almost  indefinitely  washing 
out  a  little  more  silt  from  the  sand.  Any  absolute  value,  of  course,  the 
portion  settling  between  thirty  and  ten  seconds  has  not  in  any  case,  since 
it  represents  no  distinct  pure  product  of  any  kind ;  but  even  its  relative 
amount  in  different  samples  has  no  great  precision.  Actual  results,  how- 
ever, as  given  in  the  following  analyses,  show  that  the  differences  in 
quantity  are  marked  enough  in  some  cases  to  indicate  roughly  the  amount 
of  this  product,  and  thus  to  give  some  indication  of  the  extent  of  the 
processes — in  most  cases  probably  subsequent  to  the  formation  of  the 
sediment — which  have  produced  it.  Besides,  since  the  material  is  finer 
grained  than  the  extra  fine  sand,  it  is,  in  the  end,  according  to  Thoulet's 
classification,  counted  with  the  clay  to  determine  the  amount  of  mud,  so 
that  the  separation  of  it  does  not  affect  the  final  numerical  result. 


118  THE  PETROGRAPHY  AND  GENESIS  OF  SEDIMENTS 

The  clay  washings  in  the  large  separator  funnel  were  allowed  to  settle 
for  about  half  an  hour,  the  settlings  tapped  and  rewashed  for  any  sand  or 
silt  that  might  have  escaped  the  first  washing.  The  amount,  as  indicated 
above,  was  usually  very  small.  This  method  of  separating  sand  and 
"  clay  "  is  in  principal  entirely  similar  to  the  method  of  the  Bureau  of 
Soils  of  the  U.  S.  Department  of  Agriculture.1  The  use  of  the  centrifuge 
by  the  Bureau  of  Soils  merely  hastens  settling.  Their  method  differs 
mainly  in  having  definite  size  limits  for  the  finer  portions  of  "  silt "  and 
"  clay."  But  the  analysts  of  the  Bureau  of  Soils  themselves  recognize  that 
a  perfect  separation  is  never  attained  and  that  it  is  indeed  theoretically 
possible  only  if  all  the  particles  treated  have  the  same  density  and  shape. 
But  if  other  conditions  remain  constant  the  same  result  is  attained  by 
allowing  the  particles  to  settle  a  definite  length  of  time  through  a  fixed 
distance,  so  that  theoretically  the  method  of  Thoulet,  as  used,  givfes  the 
same  results,  even  though  time  of  settling  instead  of  prevailing  size  of 
particles  settled  is  used  as  the  determining  factor. 

In  general,  it  must  be  said,  and  is  admitted  by  all  students  of  sediments, 
that  all  such  mechanical  methods  of  separating  sand  and  "  clay,"  while 
they  allow  valuable  comparison,  are,  from  a  scientific  standpoint,  still 
most  unsatisfactory.  It  is  now  generally  believed  that  the  colloidal  state, 
in  which  true  clay  may  be  assumed  to  be,  is  merely  a  certain  state  of  sub- 
division between  fairly  definite  limits  (lOO^/*  to  10/u.yu,)  in  a  continuous 
series  from  grains  visible  to  the  unaided  eye  to  molecular  solution.  If  this 
is  so,  then  any  separation  of  what  might  be  called  true  clay,  even  if  it  were 
mechanically  possible,  would  still  be  somewhat  arbitrary.  Moreover, 
there  is  some  reason  to  doubt  that  in  a  natural  sediment  there  actually 
exists  such  a  continuous  series  rather  than  a  mixture  of  certain  definite 
consituents  or  groups  of  constituents  each  with  its  own  size  limits,  the 
limits  overlapping  more  or  less. 

The  ideal  solution  of  the  problem  would  be  to  establish  a  curve  showing 
the  rate  at  which  the  settling  of  the  constituents  of  a  given  sediment 
progresses.  That  different  constituents  can  be  differentiated  in  the  finest 

1  U.  S.  Dept.  Agric.  Bureau  of  Soils,  Bull.  No.  24,  1904;  Bull.  No.  84,  1912. 


MARYLAND  GEOLOGICAL  SURVEY  119 

portion  by  this  method  is  indicated  by  the  work  of  Mohr,1  who  carries 
his  settling  to  periods  of  several  weeks.  But  he  too  separates  between  arbi- 
trary limits  and  his  curve  is  therefore  not  continuous.  Moreover,  his 
results  show  that  in  the  very  finest  portions  some  further  differentiation 
could  probably  be  made. 

To  go  into  a  more  detailed  discussion  of  methods  other  than  the 
mechanical  for  the  differentiation  of  the  constituents  of  argillaceous  sedi- 
ments would  not  be  in  place  here.  Reviews  and  discussions  of  such 
methods  can  be  found  in  a  paper  by  Stremme  and  Aarnio,  "  Die  Bestim- 
murig  der  anorganischen  Kolloide,"  etc.,  Zt.  f.  prakt.  Geol.,  vol.  xix,  1911, 
pp.  329-335,  and  van  der  Leeden  und  Schneider,  "  Ueber  neuere  Methoden 
der  Bodenanalyse  u.  der  Bestimm.  der  Kolloidstoffe  im  Boden,"  Int.  Mitt, 
f.  Bodenkunde,  vol.  ii,  1912,  pp.  81-109,  in  which,  among  others,  the 
method  of  Mitscherlich  referred  to  above  is  discussed.  There  may  also  be 
much  to  be  learned  about  the  colloidal  matter  by  the  method  of  staining 
and  microscopic  study  in  which  a  beginning  has  been  made  by  Hundes- 
hagen.2  But  it  may  be  said  in  conclusion  that  the  analysis  of  clay-bearing 
sediments  on  a  scientific  basis,  that  is,  on  the  basis  of  their  natural  con- 
stituents, has  not  yet  been  attained. 

To  continue  the  description  of  the  method  of  analysis  that  has  been 
employed  in  the  present  study,  the  clay  suspension  in  the  funnel  was 
tapped  into  a  large  evaporating  dish.  Thoulet,  who,  working  with  fresh 
modern  sediments,  was  not  obliged  to  add  ammonia  to  disintegrate,  then 
added  a  few  drops  of  alum  solution  to  precipitate  the  clay,  settled,  siphoned 
off  as  much  of  the  supernatant  water  as  possible,  and  evaporated  to  dryness 
over  a  gentle  heat.  As  ammonia  was  used  in  most  of  the  present  analyses, 
it  had  to  be  neutralized,  which  was  done  with  hydrochloric  acid.  Per- 
formed at  first  approximately,  this  neutralization  produced  irregular 
results  due  doubtless  to  solution  with  an  excess  of  acid,  while  to  neutralize 
exactly  was  very  tedious.  Moreover,  experiment  with  one  sample  showed 

1  Mohr,  E.  C.  Jul.,  Mechanische  Bodenanalyse.  Bull.  Dept.  de  1'Agr.  aux  Indes 

Neerlandaises  No.  41,  Buitenzorg,  1910,  33  pp. Ergebnisse  mech.  Analysen 

tropischer  Boden.  /bid.  No.  47,  1911,  73  pp. 

2  Hundeshagen,  Ueber  die  Anvendung  organischer  Farbstoffe  zur  diagnosti- 
schen  Faerbung  mineralischer  Substrate.  Neues  Jahrb.  f.  Min.  etc.  Beilage-Bd. 
xxviii,  1909,  pp.  335-378. 


120  THE  PETROGRAPHY  AND  GENESIS  OF  SEDIMENTS 

that  hot  water  dissolved  a  small  portion  of  it,  partly  salts,  partly  a  tough, 
almost  white,  colloidal  substance,  so  that  in  the  later  analyses  the  whole 
quantity  was  evaporated  down  on  a  steam  bath.  The  dried  clay  was 
scraped  out  of  the  dish  with  a  steel  spatula,  a  process  which  always 
involved  some  loss,  partly  from  a  small  residue  that  adhered,  partly  from 
dust  that  was  carried  away.  The  clay  was  then  dried  for  eight  hours  or 
more  at  about  105°  C.,  cooled  in  a  desiccator  and  weighed  as  rapidly  as 
possible. 

The  sand  separated  from  clay  and  silt  was  air-dried,  weighed  and  then 
passed  through  a  series  of  sives  made  of  bolting  cloth  with  approximately 
30  (28),  60,  100  (97),  and  200  meshes,  respectively,  to  the  inch.1 

Following,  according  to  Thoulet's  observations,2  are  the  minimum  sizes 
of  the  materials  held  back  by  the  different  sieves : 

=  Coarse  sand. 

30 0.89  mm. 

=  Medium  sand. 

60 0.45     ' 

=  Fine  sand. 

100 0.26     " 

=  Very  fine  sand. 

200 0.04     " 

=  Extra  fine  sand. 

Even  this  simple  process  of  sieving  is  not  quantitatively  absolute  which, 
as  indicated  above,  is  one  of  the  reasons  for  preferring  the  elutriation 
method.  The  two  causes  are :  most  important  of  all  that  the  grains  are 
not  round ;  a  minor  factor  that  the  meshes,  especially  in  the  finer  bolting 
cloths,  are  not  uniform.  As  a  result  of  the  irregular  form  of  the  grains, 
very  long  grains  with  a  short  diameter  less  than  the  mesh  opening  will 
pass,  and  with  prolonged  shaking  very  many  of  them.  The  duration  of  the 
sieving  is,  therefore,  a  matter  of  accommodation  based  largely  on  personal 
judgment  and  experience.  The  procedure  was  to  stop  when  the  grains 
that  came  through  were  predominantly  elongated.  But  this  stage  will  be 

1  The  figures  in  parentheses  are  the  given  meshes,  according  to  trade  num- 
bering, which  were  the  nearest  that  could  be  obtained.     The  actual  mesh,  ac- 
cording to  measurement,  is  still  somewhat  different,   in  most  cases  fewer 
meshes  per  inch  or  larger  openings.     Professor  Thoulet  was,  however,  good 
enough  to  assure  the  author  that  these  were  quite  accurate  enough. 

2  Thoulet,  J.,  Precis  d'analyse  (op.  cit.),  p.  64. 


MARYLAND  GEOLOGICAL  SURVEY  121 

reached  much  sooner  with  the  coarse  than  with  the  finer  sizes.  As  the 
coarse  material  was,  besides,  usually  less  abundant  the  coarsest  size  was 
not  generally  shaken  more  than  a  minute,  while  the  finest,  that  is,  that  on 
the  200-mesh  sieve,  when  it  was  abundant  required  sometimes  more  than 
half  an  hour.  The  amount  of  shaking  that  each  size  received  depended 
on  the  abundance  of  the  material  of  that  size,  the  sizes  being  successively 
removed  from  the  nest  of  sieves,  in  the  order  of  their  fineness,  while  the 
finest  was  continued  until  observation,  with  the  hand  lens,  of  the  material 
passed  showed  that  predominantly  elongated  grains  were  coming  through. 
The  sieves  were  shaken  by  hand.  The  Department  of  Agriculture  uses  a 
mechanical  shaker  in  which  the  sieves  are  left  for  about  three  minutes. 
Thoulet's  principle  is  to  continue  shaking  until  a  considerable  shaking 
passes  only  a  negligible  amount  of  material,1  as  it  would  require  an 
excessive  length  of  time  to  produce  an  absolutely  complete  separation 
of  the  finer  sizes.  But  his  limit,  which  is  also  only  approximate,  agrees 
quite  closely  with  the  present,  since,  when  dominantly  elongated  grains 
come  through,  the  rate  of  separation  is  very  slow.  The  products  of  sieving 
are  weighed  and  put  aside  for  study. 

Finally  the  "  very  fine  sands  "  are  separated  according  to  their  specific 
gravity  by  means  of  Thoulet's  solution,  of  a  density  slightly  greater 
than  2.7.  The  most  serious  defect  of  this  separation  in  the  rocks  studied 
was  due  to  the  glauconite.  Fresh  glauconite  is  lighter  than  all  the  feld- 
spar and  quartz,  so  that  it  remains  in  the  light  portion  and  can  subse- 
quently be  in  turn  separated  by  its  density.  But  in  all  the  glauconitic 
rocks  considered  in  the  following  the  greater  part  of  the  glauconite  sank 
with  the  "  heavies  "  and  was  made  up  of  grains  ranging  in  density  in 
many  cases  from  less  than  2.7  -(-  to  higher  than  3.00.  This  is  doubtless 
due  to  weathering  effects.  An  exact  determination  of  the  amount  of 
glauconite  by  weight  was  therefore  impossible,  and  even  the  fairly  close 
approximations  that  were  obtainable  with  a  solution  of  specific  gravity 
of  3.00  and  the  electro-magnet  to  be  mentioned  below,  are  not  quite  com- 
parable on  account  of  the  difference  in  density  of  the  lots  from  different 

1  Thoulet,  J.,  Precis  d'analyse  (op.  cit.),  p.  64. 


122  THE  PETROGRAPHY  AND  GENESIS  OF  SEDIMENTS 

samples.  The  importance  of  considering  the  glauconite  separately  is, 
however,  evident,  since  in  many  of  the  samples  it  has  been  formed  in  place 
and  not  brought  in  like  the  rest  of  the  material. 

Except  for  separating  the  glauconite  the  electro-magnet  plays  no 
inherent  part  in  the  analysis  of  the  samples.  It  has  been  used  merely  to 
segregate  different  minerals  in  order  to  facilitate  the  study  of  them.  The 
magnetic  permeability  of  different  minerals  is  distinct,  so  that,  by  intro- 
ducing various  resistances  in  the  circuit  of  the  magnet,  they  can  be  segre- 
gated. Thoulet  has  for  his  magnet  a  table  showing  the  current  that  will 
attract  each  mineral,  but  this  varies  so  with  the  particular  constitution, 
and  doubtless  also  with  the  amount  of  decomposition  of  the  mineral,  that 
it  affords  only  an  approximate  indication  in  practice.  It  was  found  most 
practical  to  try  different  strengths  of  current  and  examine  the  product 
with  the  hand  lens,  until  a  satisfactory  separation  was  obtained.  One  of 
the  most  refractory  minerals  in  both  the  gravity  and  magnetic  separation 
is  mica.  While  it  tends  to  accumulate  in  certain  portions,  the  segregation 
is  always  far  from  perfect,  and,  moreover,  in  transferring  it  there  are 
always  losses  said  to  be  due  to  static  electric  charges  which  cause  it  to 
adhere  to  the  surfaces  with  which  it  comes  in  contact.  This  very  static 
electric  property  can  be  used  to  separate  it  from  other  minerals,  but 
this  procedure  has  not  been  applied  in  the  present  study. 

While  the  method  thus  described  includes  all  the  steps  employed  in  a 
complete  analysis  it  appeared,  when  the  results  began  to  accumulate,  that 
some  of  the  separations  could  not  yield  information  of  any  value  in  certain 
sediments,  or  at  least  that  more  results  of  importance  could  be  accumu- 
lated by  not  making  each  analysis  so  systematically  complete ;  hence  in  a 
few  of  the  later  ones  some  of  the  steps  are  omitted. 

The  quantitative  results  of  the  mechanical  analyses  are  represented  in 
the  diagrammatic  form  (pp.  169,  170)  so  effectively  used  by  Mohr  in  the 
papers  referred  to  above.1  The  construction  of  these  diagrams  is  very 

1  While  Mohr  devised  these  diagrams  quite  independently,  exactly  the  same 
type  of  diagram,  differing  only  in  scale,  was  used  at  an  earlier  date  by  J.  A. 
Udden,  "  The  mechanical  composition  of  wind  deposits."  Augustana  Library 
Publ.  No.  1,  1898,  69  pp. 


MARYLAND  GEOLOGICAL  SURVEY  123 

simple.  The  amount  of  each  portion  is  represented  by  a  vertical  column  of 
which  the  height  corresponds  to  the  percentage  of  the  portion  present  in 
the  whole  sample.  The  columns  are  all  of  the  same  arbitrary  width  and  the 
successive  sizes  are  placed  side  by  side,  the  vertical  boundaries  between 
them  being  the  limit  of  size  that  separates  them.  Their  significance  may 
be  most  readily  conceived  by  imagining  the  columns  to  represent  small 
sample  tubes  containing  the  different  portions  and  placed  side  by  side  in 
order  of  their  size  of  grain. 

Finally,  mention  must  be  made  of  a  serious  defect  in  the  entire  analysis 
of  many  samples,  which  arises  from  the  abundance  of  carbonaceous  organic 
matter  present.  Even  a  determination  of  it  by  quantitative  analysis,  if  it 
did  not  involve  an  amount  of  time  disproportionate  to  the  advantage  to 
be  derived,  would  probably  not  give  entirely  accurate  results.  Keilhack  * 
describes  a  common  method  of  determination  by  burning  off  the  carbon- 
aceous matter,  but  this  has  so  many  defects  that  it  scarcely  seems  worth 
using.  It  is  probably  largely  on  this  account  that  the  Bureau  of  Soils  of 
the  Department  of  Agriculture  takes  no  cognizance  of  carbonaceous 
matter,  which  practice  has  been  followed  in  the  present  study.  However, 
a  specific  gravity  separation  might  be  used  here  to  float  off  the  carbon- 
aceous matter,  at  least  in  the  sands,  with  results  of  a  degree  of  accuracy 
equal  to  that  of  the  other  separations.  Certainly  in  some  of  the  sediments 
that  in  the  following  pages  have  been  called  of  the  "  delta  "  type  the  pro- 
portion of  carbonaceous  matter  is  so  great  that  it  interferes  seriously  with 
the  value  of  the  results  of  the  analyses. 

1  Keilhack,  Lehrbuch  der  praktischen  Geologic,  1908,  p.  540. 


124  THE  PETROGRAPHY  AND  GENESIS  OF  SEDI.M i:\rs 

THE  ANALYSES 

SAMPLE  NO.   1    (FIG.  A,  p.  1G!»» 
Serial  number1  :  7. 
Field  number  :   l10-10-2-1911. 
Formation  :   Magothy. 
Locality  :  Betterton. 

Appearance  :  A    compact,    massive,    homogeneous,    slightly   greenish-gray,    fine-grained, 
micaceous,  argillaceous  sand. 

MECHANICAL  ANALYSIS 
Sample    11.040  gm. 

Per  cent  of 
sample 

Sands    73.4 

Clay    26.1 

99.5 

Per  cent  of 
total  sands 

Coarse   sand    4 

Medium   sand    7.0 

Fine  sand    14.4 

Very  fine  sand    45.3 

Extra  fine  sand    33.2 

Total     100.3 

Per  cent  of 
very  fine  sand 

Light    89.3 

Heavy    10.0 

99.3 

MAGNETIC  SEPARATION  Per  cent  of 

total  heavies 

Attracted  at  2000  ohms   43.65 

S.  G.  >  3.002  15% 

S.  G.<3.002  (glauconite)  80.2%  =  32.35%  of  heavies 
=   3.20%  of  very  fine 

Attracted  at  full  current   37.10 

S.  G.<3.002  (mica)  =23.45%  of  heavies 
S.  G.>  3.002  largely  pyrite  concretions 

Non-magnetic     1.70 

Magnetite    17.40 2 

99.85 

DESCRIPTION   OF  PRODUCTS 
A.  UNDER  THE  HAND  LENS  3 

There  is  very  much  carbonaceous  plant  matter  which  gives  all  the  sands  a  dark, 
blackish-gray  appearance. 

The  coarse,  medium,  and  fine-grained  sands  all  show  a  considerable  proportion  of  well- 
rounded  and  smoothed  quartz  grains.  They  are  all  three  speckled  with  the  argillaceous 
grains  described  under  the  very  fine  light  portion,  the  proportion  of  these  increasing 
in  the  finer  portions.  Smooth  limonltic  grains  occur  in  all  of  the  portions,  perhaps  from 
the  alteration  of  glauconite  grains.  Heavy  minerals  seem  to  be  very  scarce  in  these 
coarser  portions  though  mica  is  scattered  through  the  "  fine-grained  "  sands. 

1  The  serial  number  is  the  number  given  to  the  analysis  when  it  was  made,  indicating 
the  order  in  which  the  samples  were  taken  up,  hence  not  corresponding  to  the  present 
order  which  is  stratigraphic. 

2  High  magnetite. 

3  Magnification  X  10. 


MARYLAND  GEOLOGICAL  SURVEY  125 

B.  UNDER  THE  MICROSCOPE 
/.  Very  Fine  Sand 

(1)  Light 
Ratio  of  quartz  to  feldspar  estimated  90  :  10.1 

With  the  light  portion  there  is  separated  an  abundance  of  grains  of  a  translucent  to 
opaque,  humus-brown  substance  full  of  small  dark  granules.  The  substance  is  isotropic, 
index  of  refraction  1.55-1.56.  It  crushes  plastically  under  the  knife.  Probably  it  is  a 
combination  of  organic  and  inorganic  colloidal  matter,  with  inclusions  of  granules  that 
may  be  both  mineral  and  carbonaceous  but  are  not  fresh  mineral  grains. 

(2)  Heavy 
Dominant. — Glauconite  in  worn  grains  ;  percentage  as  given. 

Abundant. — Magnetite,  garnet,  epidote,  muscovite,  pyrite  in  granular  concretions. 
Rarer. — Tourmaline,  staurolite,  chlorite,  biotite,  topaz,  lutile,  zoisite,  zircon,  enstatite, 
kyanite,  anatase  (dumortierite?). 

The  well-rounded  form  of  the  magnetite  grains  is  noteworthy. 

//.  Finer  Portions 

The  finer  portions  (extra  fine,  silt,  and  clay)  show  little  of  special  interest.  The 
clay  is  gray  with  a  strong  humus-brown  stain,  and  contains  unusually  much  of  a  dirty 
fibrous  matter  that  is  common  in  many  of  the  samples. 

Summary  and  Conclusions. — Noteworthy  are : 

(1)  The  abundance  and  variety  of  heavy  minerals. 

(2)  The  high  percentage  of  magnetite  with  associated  garnet  and 
epidote. 

(3)  The  fact  that  the  glauconite  is  all  rounded,  i.  e.,  reworked. 

(4)  The  rounded  clay-like  grains.     These  may  be  merely  undisinte- 
grated   clay,    though    their   abundance   would    seem   to   indicate    some 
concretionary  process,  perhaps  the  first  stages  in  the  formation  of  glau- 
conite, as  will  be  explained  in  the  general  discussion  of  glauconite  (see 
p.  176  below).    The  abundance  of  pyrite  in  the  sample,  however,  suggests 
that  pyrite  may  have  something  to  do  with  the  formation  of  these  granules, 
though  I  believe  such  a  process  has  not  hitherto  been  recognized. 

(5)  The  pyrite  concretions.     Pyrite  concretions  are,  under  certain 
conditions,   formed   in   waters   in   which   abundant   organic   matter   is 
decomposing. 

(6)  The  lack  of  sorting  indicated  by  the  abundance  of  several  different 
sizes  of  sand  and  the  high  percentage  of  magnetite  and  garnet. 

1  The  ratio  of  quartz  to  feldspar  was  determined  by  making  several  counts,  in  different 
parts  of  the  slide,  of  all  the  grains  in  the  field  of  view  of  a  No.  4  objective  and  deter- 
mining the  number  of  these  that  were  feldspars.  The  feldspars  were  rather  readily  picked 
out,  following  Thoulet,  with  the  aid  of  a  liquid  of  index  1.548  (the  mean  index  of  quartz), 
checked  when  necessary  by  determining  the  optical  figure.  The  average  as  will  be  seen, 
is  always  given  to  the  nearest  5  units.  The  relative  sizes  of  the  grains  was  not  con- 
sidered, so  that  the  results  have  no  absolute  quantitative  value.  They  do  serve,  how- 
ever, to  indicate  the  relative  abundance  in  different  samples. 
9 


126  THE  PETROGRAPHY  AND  GENESIS  OF  SEDIMENTS 

SAMPLE  NO.  2   (FIG.  B,  p.  169) 
Serial  number  :  10. 
Field  number  :   1MO-2-1911. 
Formation  :  Magothy. 
Locality  :  Betterton. 

Appearance  :  A  hard,  blue-gray,  faintly  laminated  clay  In  layers  about  1  Inch  thick  with 
sandy  partings. 

MECHANICAL  ANALYSIS 
Sample    .' 14.050  gm. 

Per  cent  of 
sample 

Sands    14.2 

Silt    13.2 

Clay    66.8 

Total     94.2 

Per  cent  of 
total  sands 

Coarse   sand    0.7 

Medium    sand    6.6 

Fine  sand    6.3 

Very  fine  sand    43.9 

Extra  fine  sand    42.7 

Total    100.2 

Per  cent  of 
fine  sand 

Light    87.5 

Heavy     12.4 


Total 


DESCRIPTION  OF  PRODUCTS 

A.  UNDER  THE  HAND  LENS 

The  coarse  portion  is  only  carbonaceous  matter ;  the  medium-grained  contains,  in 
addition,  small  rounded  pyrlte  nodules,  grains  and  flakes  of  argillaceous  matter,  but  as 
primary  minerals  only  a  few  flakes  of  mica.  The  fine-grained  contains  more  of  the 
clay  grains,  and  mica  more  abundant  and  in  greater  variety,  there  being  chlorite  as  well 
as  muscovite. 

B.  UNDER  THE  MICROSCOPE 

/.  Very  Fine  Sand 
(1)   Light 

Quartz  :  feldspar  =  85  :  15. 

Besides  feldspar  and  quartz  carbonaceous  fragments  and  argillaceous  grains  as  In  the 
coarser  portions,  are  important  constituents.  These  two  constituents  are,  in  fact,  so 
abundant  that  they  interfered  with  the  study  of  the  quartz  and  feldspar.  A  portion  was 
therefore  incinerated  and  with  the  aid  of  this  incinerated  portion  the  following  facts 
could  be  determined. 

The  plant  fragments  appear  in  two  forms,  one  black  and  opaque,  the  other  brown, 
translucent,  and  generally  showing  some  organic  structure.  The  Incinerated  portion 
turned  from  black  to  red.  Under  the  microscope  it  was  then  found  that  most  of  the 
opaque  black  fragments  bad  disappeared  but.  the  brown  translucent  remained  with  all 
their  structure,  having  apparently  only  turned  red.  It  may  be  that  some  of  the  trans- 
lucent had  also  disappeared  but  the  essential  point  Is  that  many  of  them,  at  least,  were 
evidently  permeated,  or  perhaps  partly  replaced,  by  some  Iron  salt  which  on  incineration 
preserved  the  form  of  the  original  plant  fragment. 

Here  too  the  clay  grains,  found  in  the  other  portions  as  well,  could  be  studied  under 
the  microscope.  The  facts  about  them  may  therefore  be  summarized.  They  are  round 


MARYLAND  GEOLOGICAL  SURVEY  127 

or  flaky  In  form.  The  smaller  sizes  are  translucent,  of  a  humus-brown  color,  filled  with 
small  opaque  flakes  and  grains.  They  crush  plastically  but  the  crushed  portion  reveals 
no  new  characters. 

Essentially  they  are  probably  true  clay  and  their  appearance  Is  that  of  the  greater 
part  of  what  Is  separated  as  clay.  But  it  Is  Important  to  know  whether  they  are  merely 
undisintegrated  portions  of  clay,  or  whether  they  are  minute  concretions.  The  flaky 
form  of  many  of  them  supports  this  latter  hypothesis,  suggesting  their  formation  in 
moulds  such  as  the  plant  fragments  might  afford.  For  the  present,  however,  the  ques- 
tion must  remain  undecided. 

(2)    Heavy 

The  heavy  minerals  are  : 

Abundant. — Muscovite,   chlorite,   serpentine. 

Rarer. — Tourmaline,  glauconite,  garnet. 

Essentially  the  heavy  portion  is  muscovite,  with  some  chlorite  and  serpentine, 
tourmaline  and  garnet  being  exceedingly  rare.  Of  glauconite  there  are  very  few  grains, 
many  of  them  weathered  yellow. 

//.  Silt 

Dark  dirty,  brownish-black,  micaceous.  The  dark  color  appears  to  be  due  mainly  to 
the  great  amount  of  black  carbonaceous  matter  which  is  probably  responsible  for  the 
high  percentage  of  silt  separated  from  this  sample,  though  the  large  proportion  of  the 
finest-grained  sands  is  probably  also  a  factor  in  this  result.  The  carbonaceous  matter 
not  only  contributes  to  the  silt  itself  but  also  catches  up  many  grains  of  fine  sand  which 
are  floated  off  with  It.  There  is  very  little  argillaceous  matter  and  that  in  irregular 
flocules,  not  in  the  rounded  grains  noted  in  the.  very  fine  light  portion. 

Summary  and  Conclusions. — Noteworthy  are : 

(1)  The  very  small  proportion  of  sands  and  the  large  proportion  of 
clay. 

(2)  The  very  high  proportion  of  carbonaceous  matter. 

(3)  The  granules  of  argillaceous  matter  and  the  pyrite  concretions 
as  in  sample  1.    The  sample  seems  to  be,  like  sample  1,  high  in  heavy 
minerals,  but  this  is  deceptive  since  micas  are  the  principal  constituent  of 
the  heavy  portion,  and  these  in  spite  of  their  specific  gravity  are  classed, 
in  the  processes  of  sedimentation,  rather  with  the  light  and  fine-grained 
minerals. 

SAMPLES  NO.   1   AND  NO.   2 

General  Summary  and  Conclusions. — While  sample  2  is  markedly  dif- 
ferent from  sample  1  in  the  much  lower  percentage  of  sand,  in  the  general 
dominance  of  the  fine-grained  materials,  and  in  the  scarcity  of  heavy 
minerals  other  than  mica,  it  still  has  in  common  with  it  certain  features 
that  are  essential.  Foremost  among  these  is  the  wide  range  of  size  in  the 
sands ;  for  while  these  are  dominantly  finer-grained  they  do  not  show  that 
dominance  of  any  one  size  that  is  characteristic  of  the  most  typical  marine 
sediments  which  have  been  subjected  to  the  sorting  action  of  strong  waves. 
This  is  at  once  apparent  from  an  inspection  of  the  diagrams  of  these  two 


128  THE  PETROGRAPHY  AND  GENESIS  OF  SEDIMENTS 

sediments  (A)  and  (B),  p.  169,  with  the  diagrams  on  p.  170,  representing 
various  types  of  deposits.  The  high  percentage  of  carbonaceous  matter  is 
also  a  characteristic  of  both  samples.  Both  contain  concretionary  pyrite 
grains  or  small  nodules,  and  in  both  there  are  the  peculiar  clay  granules 
that  have  been  noted. 

Before  interpretation  of  the  beds  is  attempted  their  manner  of  occur- 
rence in  the  field  should  be  taken  into  account.  This  is  characterized 
above  all  by  the  rapid  and  rather  extreme  alternation  of  the  beds  between 
the  two  types,  sandy  and  argillaceous,  as  fairly  well  represented  by  these 
two  samples.  Carbonaceous  matter  is  conspicuous,  also  micaceous  beds, 
while  thin  films  of  whitish  sand  between  the  beds  are  a  characteristic 
peculiarity. 

The  mechanical  analyses  of  sediments,  that  are  represented  on  p.  170, 
are  not  numerous  enough  nor  sufficiently  correlated  with  the  exact  condi- 
tions of  their  formation  to  justify  direct  matching  of  the  above  analyses 
with  them.  They  illustrate  certain  general  factors  in  sedimentation  rather 
than  definite  types  of  sediment,  and  this  first  discussion  of  them  may 
therefore  be  made  a  general  introduction. 

The  principal  factors  in  the  diagrams  are:  (1)  The  maximum,  that  is, 
the  predominant  portion.  Both  the  extent  to  which  it  exceeds  the  other 
portions  as  an  indication  of  the  degree  of  sorting  of  the  sediment,  and  the 
size  which  it  represents  as  indicating  the  strength  of  the  sorting  agent  are 
significant.  (2)  The  sharpness  of  the  "  curve''  as  Mohr  calls  it,  on  each 
side  of  the  maximum,  that  is,  the  extent  to  which  the  maximum  exceeds 
the  portions  on  both  sides  of  it.  (3)  The  general  form  of  the  curve,  espe- 
cially whether  it  shows  more  than  one  maximum.  This  last  feature,  how- 
ever, while  theoretically  important  is  evidently  very  much  influenced  by 
the  degree  and  limits  of  subdivision  of  the  sample.  In  the  diagrams  of 
these  Cretaceous  sediments  the  only  second  maximum  is  that  representing 
the  clay  portion,  but  that  this  would  in  most  cases  probably  disappear  is 
indicated  by  the  analyses  given  by  Mohr.1  He  makes  many  subdivisions 
of  the  portion  classed  as  clay  in  Thoulet's  method  of  analysis,  with  the 
result  that  there  is  often  a  steady  fall  of  the  curve  through  these  portions. 

1  Mohr,  E.  C.  Jul.,  Ergebnisse  mech.  analysen,  etc.  (op.  cit). 


MARYLAND  GEOLOGICAL  SURVEY  129 

An  examination  of  the  diagrams  on  p.  170  leads  to  the  recognition  of  the 
following  general  effect  of  different  conditions  and  agents  on  the  diagrams. 
Most  conspicuous  is  the  difference  in  the  degree  of  sorting  or  sizing.  The 
most  complete  sizing  is  produced  by  strong  waves  and  by  wind  action 
(p.  170,  figs.  A,  C,  J,  K,  L).  Off-shore  marine  sediments  (p.  170, 
fig.  C)  are  as  well  sorted  as  beach  sands,  differing  only  in  having  the 
maximum  in  a  finer  size.  A  similar  difference  in  the  maximum  appears 
between  dune  sands  of  temperate  regions  (p.  170,  fig.  J)  and  those  of 
tropical  regions  (K,  L),  and  though  this  might  be  due  to  a  difference  in 
the  part  of  the  dunes  from  which  the  different  samples  were  taken,  it  is 
also  quite  possible  that  the  prevailing  winds  of  these  tropical  regions  are 
stronger. 

But  while  the  deposits  found  respectively  under  the  influence  of  winds 
and  of  strong  waves  thus  agree  in  their  perfection  of  sizing,  they  also 
show  a  certain  difference  in  that,  in  the  product  of  wave  action,  after  the 
maximum  the  largest  portion  is  the  next  finest  material,  while  in  the 
eolian  deposit  the  next  coarsest  is  generally  the  largest.1 

The  lagoonal  deposits  may  be  taken  as  representing  in  general  deposits 
in  a  small  body  of  water  in  which  there  is  much  weaker  wave-action  and 
less  room  for  the  horizontal  separation  of  sizes  than  in  the  ocean.  Conse- 
quently sizing  is  less  perfect  (p.  170,  figs.  .E,  F). 

Eiver  sediments  in  addition  to  being  poorly  sized  tend,  as  explained  by 
Mohr,2  to  show  an  abrupt  rise  of  the  curve  on  the  left  and  a  gentle  fall 
on  the  right.  That  is,  sedimentation  of  streams  is  likely  to  take  place 
from  a  sudden  change  in  velocity ;  hence  all  of  the  coarsest  and  much  of 
the  finer  material  that  it  has  been  able  to  carry  to  the  point  of  sedimenta- 
tion will  suddenly  drop  out.  This  is  well  illustrated  by  the  typical  dia- 
gram, M,  p.  170. 

Delta  deposits  show  a  combination  of  this  stream  effect  with  a  certain 
amount  of  sorting  as  can  be  seen  in  diagrams  D  and  I,  pi.  II,  but  the  sort- 
ing effect  of  wave  action  appears  very  rapidly  away  from  the  edge  of  a 
marine  delta.3 

1  See  further,  Udden,  J.  A.,  The  mechanical  composition  of  wind  deposits. 
Augustana  Library  Publ.  No.  1,  1898. 

2  Mohr,  E.  C.  Jul.,  Ergebnisse  mechanischer  analysen,  etc.  (op.  cit.),  p.  35. 

3  See  some  of  the  analyses  in  Thoulet's  study  of  the  Gulf  of  Lyon,  cited 
above. 


130  THE  PETROGRAPHY  AND  GENESIS  OF  SEDIMENTS 

This  general  view  of  sedimentation  diagrams  affords  a  sufficient  basis 
for  the  special  consideration  of  the  sediments  discussed  in  this  chapter, 
To  turn  then  to  samples  1  and  2. 

No  detailed  field  and  laboratory  study  of  delta  sediments  has  been  pub- 
lished, to  the  writer's  knowledge ;  but  from  what  little  can  be  learned  of 
such  deposits  it  appears  that  the  beds  from  which  samples  1  and  2  are 
taken  show  many  of  the  characteristics  of  delta  formations.  In  their  field 
relations  the  rapid  alternation,  the  extremes  represented,  the  thin  partings 
of  sand,  and  the  abundance  of  carbonaceous  matter  support  this  view. 
And  consideration  of  the  conditions  of  sedimentation  in  a  delta  leads  to 
the  same  conclusion,  for,  according  to  the  principle  laid  down  by  Johannes 
Walther,  only  such  facies  can  succeed  each  other  as  can  exist  side  by  side. 
Now,  in  a  delta  there  is  a  sharp  difference  between  the  channels  and  the 
waters  lying  to  the  side  of  them,  so  that  in  one  there  would  be  deposited 
relatively  coarse  sand,  while  in  the  other  fine  sediments  would  slowly 
settle.  Then  sudden  changes  of  channel,  such  as  would  be  produced  by 
high  water  in  a  region  with  the  extremely  low  relief  of  a  delta,  would  bring 
two  such  facies  into  vertical  succession,  producing  the  type  of  section  seen 
at  this  locality.  The  sandy  partings,  on  the  other  hand,  would  result 
merely  from  the  passing  conditions  of  a  single  flood  without  a  change  of 
channel. 

The  mechanical  analyses,  also,  fall  in  with  this  general  view.  To  be 
sure,  A,  p.  169  (=  sample  1)  and  E,  p.  170  (  =  a  lagoon  sediment)  show  a 
similarity  which  amounts  almost  to  identity.  But  the  quiet,  open  bodies  of 
water  in  a  delta  would,  in  their  conditions  of  sedimentation,  be  entirely 
equivalent  to  a  lagoon,  like  that  from  which  E,  p.  170,  is  derived.  In  B, 
p.  169,  the  upper  shaded  portions  of  the  five  left-hand  columns  represent 
the  analysis  recalculated  to  a  basis  of  100  after  subtracting  the  clay  and 
silt,  and  in  this  form  the  similarity  of  the  diagram  to  a  stream  sediment 
like  M,  p.  170,  with  the  abrupt  rise  of  the  curve  on  the  left  and  the  poor 
sorting,  is  strikingly  brought  out.  Both  these  analyses  therefore  fit  in  well 
with  the  conditions  that  would  exist  in  a  broad  delta. 

Formation  of  pyrite  is  another  characteristic  of  such  deposits.  It  is 
due,  as  noted  above  ( Sample  No.  1,  Summary  and  Conclusions),  to  the  1LS 


MARYLAND  GEOLOGICAL  SURVEY  131 

liberated  by  the  decay  of  organic  matter,  but  requires  slow  circulation  of 
the  water  in  which  the  H2S  is  liberated,  so  that  the  gas  may  not  be  carried 
off  as  quickly  as  it  is  formed.  Thus  pyrite  grains  are  characteristic  of  the 
deeper,  stagnant  water  of  the  Black  Sea,  and  the  writer  has  a  carbonized 
fragment  of  wood  collected  from  the  East  Kiver  at  New  York,  encrusted 
with  pyrite.  The  pyrite  grains  in  the  coarsest  sediment  (sample  1) 
were  therefore  probably  carried  into  it  from  some  stagnant  portion  of  the 
delta  invaded  by  a  change  of  current. 

A  peculiar  feature,  perhaps  related  to  the  pyrite  formation,  was  noted 
in  the  "  light "  portion  of  sample  No.  2.  Black  opaque,  and  brown  trans- 
lucent carbonaceous  matter  was  so  abundant  that  a  portion  was  inciner- 
ated to  free  it  from  these  particles.  The  effect  of  incineration  was  to  give 
the  sample  a  reddish  color,  but  a  large  part  of  the  organic  fragments 
remained.  Evidently  then  they  had  been  impregnated  or  partly  replaced 
by  some  iron  salt,  very  possibly  by  pyrite. 

Some  such  process  may  also  account  for  the  abundant  clay  granules 
noted  in  both  samples.  The  flat  form  of  many  of  these  is  against  the 
assumption  that  they  are  merely  undecomposed  clay  fragments,  since  in 
that  case  they  would  more  probably  have  been  developed,  in  shaking,  with 
rounded  form.  The  flat  shape  indicates  rather  that  they  were  formed  in 
some  mould  with  that  shape,  perhaps  in  the  carbonaceous  plant  fragments, 
where  they  may  well  have  shared  in  the  impregnation  with  an  iron  salt 
shown  by  the  plant  fragments  themselves.  This  problem,  however, 
requires  further  study.  The  facts  are,  as  far  as  I  know,  new. 

Of  great  geologic  interest,  though  not  bearing  immediately  on  the  con- 
ditions of  origin  of  this  deposit,  is  the  occurrence  of  glauconite  in  both  of 
the  samples.  It  shows  that  conditions  favorable  to  the  formation  of  glau- 
conite existed  previously  even  farther  inland  than  this  region.  Since  there 
is  no  trace  of  a  glauconitic  deposit,  older  than  these  beds,  known  in  the 
region,  there  must  have  been  a  considerable  transgression  in  early 
jMagothy  or  pre-Magothy  times  of  which  the  deposits  have  been  subse- 
quently entirely  eroded. 

It  is  further  worth  noting,  though  without  much  more  extensive  field 
study  the  fact  must  not  be  given  too  much  weight,  that  this  particular 


132  THE  PETROGRAPHY  AND  GENESIS  OF  SEDIMENTS 

facies  of  the  Magothy  occurs  here  at  the  head  of  Chesapeake  Bay,  there- 
fore just  below  the  mouth  of  the  present  Susquehanna.  It  points  to  the 
possible  existence  of  that  stream  in  Cretaceous  times. 

SAMPLE  NO.  3    (FIG.  C,  p.  169) 
Serial  number  :   13. 
Field  number  :  3-7-13-1911. 
Formation  :  Matawan. 

Locality  :  Chesapeake  and  Delaware  Canal. 
Appearance  :  Typical  Matawan  ;  black  glauconitic  clay  with  little  mica. 

MECHANICAL  ANALYSIS 
Sample    8.967  gm. 

Per  cent  of 
sample 

Sands »    64.8 

Silt     6.3 

Clay    27.0 


Total 


Per  cent  of 
total  sands 


Coarse  sand 4.8 

Medium  sand    5.3 

Fine  sand    „ 5.7 

Very  fine  sand 59.4 

Extra  fine  sand   24.8 

Total     100.0  » 

Per  cent  of 
very  fine  sand 

Light     71.2 

Heavy    26.3 

Total     97.5 

MAGNETIC  SEPABATIOX 

Per  cent  of 
heavies 

Attracted  at  2000  ohms   (glauconite)  2 63.7    =16.8%  of  very  fine 

Attracted   at   full    current 28.6"] 

Xon-magnetic    0.5  U   8.8%  of  very  fine 

Magnetite    2.9  J 

Total     95.7 

Per  cent  of 
2000-ohms 
portion 

Attracted  at  2000  ohms,  S.  G.  >  3.002 12.0 

Attracted  at  2000  ohms,  S.  G.<  3.002  (glauconite)  2 87.1  =  14.6%  of  very  fine 


Total 


1  Total  sands  by  summation  of  parts. 

*  The  separation  with  the  solution  of  density  3.002  was  made  to  facilitate  study  of 
the  rare  heavy  minerals.  A  small  part  of  the  glauconite  came  down  with  tho  heavy 
minerals  while  much  mica  remained  floating  with  the  glauconite.  The  value  for  per- 
centage of  glauconite  after  the  separation  at  density  3.002  is,  however,  probably  nearer 
right  than  before  this  separation,  so  that  ylauconite  may  be  taken  as  about  15%  of  the 
very  fine  sand,  leaving  about  11%  of  true  heavy  minerals. 


MARYLAND  GEOLOGICAL  SURVEY  133 

DESCRIPTION  OF  PRODUCTS 

A.  UNDEE  THE  HAND  LENS 

7.  Coarse  Sand 

(a)  Fairly  well  rounded  grains  of  quartz  mostly  white  opaque,  almost  all,  however, 
much  pitted  and  corroded  as  if  by  solution. 

(b)  Next   in   abundance   are   rounded   concretions   formed  of  grains   of   fresh-looking 
glauconite,  quartz,  etc.,  cemented  by  limonitic  matter. 

(c)  Some  of  the  quartz  is  of  the  black  granular  concretionary  type  (cf.  Sample  No.  13) 
suggesting  secondary  origin  in  the  sediment. 

77.  Medium  Sand 

(a)  Angular  quartz  grains  predominate,  though  there  are  still  some  very  well  rounded ; 
there  is  also  more  glassy,  less  opaque  quartz. 

(b)  The  glauconite  is  mostly  in  rounded  grains ;  most  of  those  that  are  not  rounded 
suggest    by    the    irregularity    of    their    form    a    secondary    concretionary    origin    from 
botryoidal  grains.     There  are  a  very  few  normal  botryoidal  grains  all  somewhat  rounded. 
The  proportion  of  glauconite  is  small. 

(c)  There  are  limonitic  sand  concretions  as  in  the  coarse  sand  but  more  rough  and 
irregular,  less  rounded. 

(d)  Considerable  white  mica. 

(e)  Black  carbonaceous  fragments. 

(f)  Shell  (?)  fragments  stained  brown. 

777.  Fine  Sand 
Its  general  appearance  is  dark  greenish-black,  speckled. 

(a)  Quartz  predominantly  glassy  and  angular. 

(b)  Glauconite  as  in  preceding  but  much  more  abundant. 

(c)  Limonitic  sand  concretions  as  in  preceding. 

(d)  Much  white  mica. 

(e)  Many  black  carbonaceous  fragments. 

IV.   Very   Fine  Sand 
General  appearance  much  like  the  fine  sand. 

V.  Extra  Fine  Sand 
Dark  blackish-gray.  Appear  much  like  the  preceding  portion. 

B.  UNDER  THE  MICROSCOPE 

7.  Very  Fine  Sand 

(1)  Light 
Quartz  :  feldspar  =  90  :  10 

The  feldspars  appear  unusually  decomposed.     No  plagioclase  was  found. 
There  is  little  glauconite  and  mica  left. 
Both  quartz  and  feldspar  show  much  ocherous  staining. 

A  grain  was  noted  made  up  of  individual  grains  of  quartz  differently  oriented  in  a 
cloudy  quartz  cement  of  homogeneous  orientation,  believed  to  be  derived  from  quartzite. 

(2)  Heavy 

(a)  Attracted  at  2000  ohms  heavier  than  3.002. 

The  abundant  minerals,  in  the  approximate  order  of  their  frequency,  are  : 
Abundant. — Glauconite  in   translucent   to   nearly  opaque   olive-green   grains,   chlorite, 
biotite  unusually  abundant,  epidote. 

Rarer. — Garnet,  tourmaline,  muscovite,  staurolite,  rutile. 

(b)  Attracted  at  2000  ohms  lighter  than  3.002. 

Not  especially  studied.  Almost  pure  glauconite  with  some  mica. 

(c)  Full-current  product. 

A  brownish-yellow,  micaceous  sand. 

Abundant. — Muscovite,  chlorite,  quartz.  This  is  doubtless  separated  here  on  account  of 
its  heavy  ocherous  stain. 

Rarer. — Tourmaline,  epidote,  biotite,  asbestos  (?). 


134  THE  PETROGRAPHY  AND  GENESIS  OF  SEDIMENTS 

(d)  Non-magnetic. 

Zircon  and  enstatlte,  about  equally  abundant.    Kyanlte  very  rare. 

(e)  Attracted  by  permanent  magnet :    Mainly  magnetite  but  with  much  chlorite,  some 
biotlte,  and  a  little  glauconite.     Magnetite  In  very  angular  grains. 

//.  Extra  Fine  Sand 
Mainly  quartz  with  some  glauconite   and   mica. 

II I.  Silt 

Dark  gray  with  a  yellowish  tint.  Many  limonite  flakes.  Much  mica.  A  fibrous 
serpentinous  mineral  common. 

IV.  Clay 

Yellowish  showing  much  limonitic  matter.     Much  fibrous  matter. 

Summary  and  Conclusions. — The  most  striking  feature  of  this  bed  is 
the  evidence  of  reworking  of  the  material  in  it.  Thus,  except  in  the 
coarsest  sand,  there  is  almost  no  glauconite  in  primary  botryoidal  form, 
the  grains  being  mostly  rounded. 

I  think  the  ocherous  stain  of  the  grains  throughout,  the  sand-ocher 
concretions,  and  the  weathered  condition  of  the  feldspars  may  be  inter- 
preted in  the  same  way,  for  it  does  not  seem  as  though  such  products 
could  be  formed  in  a  sediment  as  argillaceous  as  this  while,  moreover,  the 
bed  itself  remained  black  and  free  from  ocherous  stain.  It  seems  more 
probable  that  they  originated  in  a  more  open-textured  glauconitic  sand 
exposed  to  atmospheric  agents  before  its  constituents  were  reworked  and 
redeposited  in  this  bed. 

The  other  principal  feature  is  the  evidence  that  seems  to  me  to  point 
to  something  like  a  delta  facies  for  this  bed.  The  factors  indicating 
this  are : 

1.  The  mechanical  composition  of  the  sediment  as  shown  in  C,  p.  169 
(cf.  D  and  J,  p.  170).    The  material  is  seen  to  be  unsorted,  all  sizes  being 
well  represented,  though  the  three  finest  largely  predominate.    This  poor 
sorting  suggests  a  small  body  of  water,  either  a  lagoon  or  a  quiet  open 
stretch  of  water  in  a  delta,  while  the  sharp  rise  of  the  curve  from  the  fine 
to  the  very  fine  sand  with  a  slow  drop  to  the  right  has  been  shown  in  the 
general  discussion  of  these  diagrams  to  be  characteristic  of  stream  sedi- 
ments. 

2.  The  abundance  of  mica. 

3.  Abundance  of  carbonaceous  matter. 


MARYLAND  GEOLOGICAL  SURVEY  135 

4.  The  high  percentage  of  heavy  minerals,  especially  the  rather  large 
proportion  of  magnetite. 

Finally,  there  are  to  be  especially  noted  the  black  concretionary  quartz 
grains  which,  for  the  present,  I  shall  not  discuss  (see  p.  175,  below). 

SAMPLE   NO.  4    (FIG.   D,  p.  169) 
Serial  number  :   14. 
Field  number  :  4-7-13-1911. 
Formation  :  Matawan. 

Locality  :  Chesapeake  and  Delaware  Canal. 

Appearance  :  A   fairly   light-gray,    very   micaceous,    fine-grained,    argillaceous   sand ;    no 
glauconite  apparent. 

MECHANICAL  ANALYSIS 
Sample    7.510  gm. 

Per  cent  of 
sample 

Sands    68.1 

Silt    1.1 

Clay    29.5 

Total 98.7 

Per  cent  of 
total  sands 

Coarse  sand    0.4 

Medium  sand    1.4 

Fine   sand    3.1 

Very  fine  sand    72.8 

Extra   fine  sand    21.4 

Total     99.1 

Per  cent  of 
very  fine  sand 

Light    88.4 

Heavy    9.8 

Total    .  .  .    98.2 


MAGNETIC  SEPARATION 

Magnetic    98.1 

Non-magnetic    ") 
Magnetite          J  " 

Total     .  ..100.0 


DESCRIPTION  OF  PRODUCTS 
A.  UNDER  THE  HAND  LENS 

/.  Coarse  Sand 
Consists  of  13  flakes  of  white  mica  and  one  very  lustrous  black  carbonaceous  flake. 

//.  Medium  Sand 

Almost  all  mica,  mostly  white  with  some  brown  and  pale  green  flakes.     Carbonaceous 
grains.    No  quartz  could  be  found. 

///.  Fine  Sand 
Same  composition  as  the  preceding. 

IV.  Very  Fine  Sand 
See  microscopic  study  of  parts. 


136  THE  PETROGRAPHY  AND  GENESIS  OF  SEDIMENTS 

V.  Extra  Fine  Sand 
Dirty  green  micaceous  sand. 

B.  UNDEK  THE  MICROSCOPE 
I.  Very  Fine  Sand 

(1)  Light 
Quartz  :  feldspar=85  :  15 

General  appearance  silvery-gray,  micaceous. 
The  quartz  grains  are  of  two  kinds : 

(a)  Glassy  grains  with  more  or  less  Inclusions. 

(b)  Rough,    pitted,   granular   fragments    with   a   greenish   tinge.      The  green-stained 
variety  is,  however,  rare. 

Glauconite  occurs  in  pale,  olive-green,  transparent,  rounded  grains,  very  fresh  looking. 
All  kinds  of  feldspars  except  plagioclases  were  noted,   in   general   appearing  rather 
rough  and  weathered  but  not  kaolinized. 

(2)  Heavy 
(a)   Magnetic 

General  appearance  light  greenish-drab,  with  much  muscovite  and  a  striking  absence 
of  glauconite  and  generally  of  dark  minerals. 

Dominant. — Muscovite,  chlorite,  glauconite,  serpentine. 

Subsidiary. — Garnet,  tourmaline,  biotite,  calcite   (?). 

The  biotite  appears  much  decomposed,  some  of  it  full  of  black  grains  (magnetite   ?). 

(b)    Non-magnetic 
Dominant. — Zircon. 
Rare. — Enstatite,  garnet,   calcite,  kyanite. 

//.  Extra  Fine  Sand 
Appearance.    Silver-gray  with  a  greenish  tinge. 

(1)  Much  glauconite  in  round  grains,  green,  semi-transparent,  fresh-looking. 

(2)  Round,  brownish  grains   specked  with  black.     They  look  exactly   like  clay  but 
polarize  faintly.     They  differ  from  the  glauconite  in  that  the  glauconite  is  clear  without 
the  black,  granular  inclusions.     (Cf.  Silt  (III)  below.)  ' 

///.  Silt 

(1)  Much  argillaceous  material  in  flakes  or  globules. 

(2)  Rounded  grains  of  transparent,  granular,  clay-like  material  of  which  the  globular 
form  and  aggregate  polarization  suggest  that  it  may  be  incipient  glauconite. 

(3)  Pale,  yellowish-green,  transparent  glauconite. 

(4)  A  few  pale  yellow,  transparent,  angular,  granular,  non-polarizing  flakes,  probably 
of  limonite. 

(5)  Mineral  grains  are  common. 

(6)  There  are  large  flakes  of  mica. 

(7)  Black  carbonaceous  matter. 

IV.  Clay 

Appearance  blue-gray. 

Pretty  fine  clay  with  much  fibrous  material  which  though  dirty  brown  and  clay-like  in 
appearance  yet  polarizes. 

The  amorphous-looking  clay  also  polarizes  as  an  aggregate,  probably  on  account  of 
minute  included  mineral  fragments.  Individual  mineral  grains  are,  however,  unusually 
scarce. 

Summary  and  Conclusions. — Two  characters  are  particularly  striking 
in  this  sediment. 

(1)  The  foremost  is  the  abundance  of  mica  apparent  in  the  original 
specimen,  but  supplemented  in  the  analysis  by  the  high  percentage  of  the 

*Note  that  the  clay  was  also  found  to  have  aggregate  polarization  though  that  may 
have  been  due  to  included  mineral  fragments. 


MARYLAND  GEOLOGICAL  SURVEY  137 

fine-grained  portions  with  which  it  goes  in  sedimentation,  and  the  low 
proportion  of  heavy  minerals,  yet  without  a  very  high  percentage  of  clay. 

(2)  The  second  important  feature  is  the  apparent  secondary  character 
of  the  glauconite.     There  are  no  botryoidal  grains,  all  those  that  occur 
being  rounded,  and  occurring  only  in  the  very  fine-grained  and  finer 
portions. 

Furthermore  there  is  to  be  noted : 

(3)  The  abundance  of  carbonaceous  matter. 

(4)  The  weathered  condition  of  the  feldspars. 

(5)  The  abundance  of  biotite. 

Of  great  general  interest  as  bearing  on  the  problem  of  the  origin  of 
glauconite  are  the  rounded  grains  of  substance  having  the  appearance  of 
clay  and  yet  polarizing,  suggesting  a  transition  form  between  clay  and 
glauconite.  I  shall  take  these  up  later  in  a  general  discussion  of  the 
glauconite  below.  ( See  p.  176,  below) . 

SAMPLE   NO.  5    (FIG.   E,  p.  169) 
Serial  number  :   11. 
Field  number  :  1-7-13-1911. 
Formation  :  Matawan. 

Locality  :  Chesapeake  and  Delaware  Canal. 
Appearance  :  Yellow,  micaceous  and  slightly  glauconitic  _sand. 

MECHANICAL  ANALYSIS 
Sample 8.395  gm. 

Per  cent  of 
sample 

Sands  1   92.6 

"  Clay  "  (mainly  yellow  ocher) 7.7 


Total   100.3 

Per  cent  of 
total  sands 

Coarse  sand 0.2 

Medium  sand 2.8 

Fine  sand 24.9 

Very  fine  sand 69.0 

Extra  fine  sand 3.1 

Total    100.0  * 

Per  cent  of 
very  find  sand 

Light    90.4 

Heavy    8.6 

Total    99.0 

1  Total  sands  by  summation  of  parts. 


138  THE  PETROGRAPHY  AND  GENESIS  OF  SEDIMENTS 


MAGNETIC  SEPARATION 

Per  cent  of 
total  heavies 

Attracted  at  2000  ohms  (glauconlte) 52.2 

Attracted  at  1000  ohms 9.8 

Attracted  at  200  ohms  (mica) 35.9 

Total    97.9 

Magnetite  and  non-magnetite  each  about  1  per  cent. 

DESCRIPTION  OF  PRODUCTS 

A.  UNDER  THE  HAND  LENS 

/.  Coarse  Sand 

Eight  grains  of  quartz,  of  which  two  are  well  rounded,  the  others  fractured,  more  or 
less  angular  and  rough.  Here  again  It  seems  as  If  the  roughness  might  in  part  be  due 
to  solution  acting  on  the  grains. 

II.  Medium  Sand 

Striking  for  the  angularity  of  the  quartz  grains,  though  their  surface  is  nevertheless 
glossy,  again  suggesting  the  action  of  solution.  Yellowish-green  glauconlte  with 
primary  botryoidal  form  is  present.  There  is  some  ocherous  staining. 

//.  Fine  Sand 
In  general  the  same  as  the  medium  sands  with  perhaps  slightly  more  glauconite. 

IV.  Very  Fine  Sand 

In  this  size  the  glauconlte  grains  are  in  general  worn,  and  there  are  many  limonitic 
grains. 

V.  Extra  Fine  Sand 
Very  limonitic. 

/.  Very  Fine  Sand 
I.  Very  Fine 

(1)  Light 
Quartz  :  feldspar  =  90  :  10. 

The  grains  of  both  quartz  and  feldspar  have  much  glauconite  adhering  to  their 
surfaces  and  penetrating  Into  their  fissures.  There  are  some  rusty,  round  grains  of 
glauconite  present. 

(2)  Heavy 

(a)  Attracted   at   2000  Ohms 

Mostly  glauconite  in  rounded  grains,  some  translucent  brown,  others  semi-opaque, 
dirty,  greenish-yellow. 

Accessory. — Chlorite,  epidote,  tourmaline. 

(b)  Attracted  at  1000  Ohms 

Has  a  golden  brown  slightly  green-tinged  color,  from  an  abundance  of  completely 
yellow  glauconite. 

Accessory. — Tourmaline,  epidote,  biotlte. 

(c)  Attracted  at  200  Ohms 

Appearance  golden-brown,  micaceous.     Almost  all  biotite  generally  pale  yellow. 
Accessory. — Serpentine,  tourmaline. 

(d)  Full  Current 
Mainly  mica  and  some  enstatite. 

(e)  Non-magnetic 
Most  Common. — Enstatite. 

Rarer. — Zircon,  rutile. 


MARYLAND  GEOLOGICAL  SURVEY  139 

Summary  of  Heavy  Minerals 
Dominant. — Glauconite,   biotite. 

Rarer. — Chlorite,  epidote,  muscovite,  magnetite,  tourmaline,  serpentine,  enstatlte, 
zircon,  rutile. 

//.   Clay 
Very  limonitic  but  also  with  a  considerable  fibrous  portion. 

Summary  and  Conclusions. — In  spite  of  the  fact  that  this  is  a  rather 
pure  sand  with  little  clay  the  proportion  of  the  finer  sizes  of  sand,  espe- 
cially of  the  very  fine,  is  remarkably  large. 

The  proportion  of  heavy  minerals  is  insignificant;  for  if  from  the  small 
percentage  that  settled  at  2.7  -f-  is  deducted  the  glauconite  there  remains 
principally  biotite,  which  in  spite  of  its  specific  gravity  is  not  properly 
regarded  as  a  heavy  mineral. 

The  botryoidal  form  of  the  glauconite  in  this  sample  indicates  that  it 
has  been  formed  in  place.  The  large  proportion  of  glauconite  is  unusual. 

SAMPLE  NO.  6    (FIG.  F,  p.  169) 
Serial  number  :   12. 
Field  number  :  2-7-13-1911. 
Formation  :  Matawan. 

Locality  :  Chesapeake  and  Delaware  Canal. 

Appearance  :  Typical  Matawan  of  Maryland.     A  dark-gray,  friable,  fine-grained,   some- 
what argillaceous  sand,  showing  glauconite  under  the  hand  lens. 

MECHANICAL  ANALYSIS 
Sample    9.867  gm. 

Per  cent  of 
sample 

Sands    75.4 

Silt    2.2 

Clay     21.2 

Total    98.8 

Per  cent  of 
total  sands 

Coarse  sand 1.7 

Medium  sand    9.3 

Fine  sand   32.6 

Very   fine  sand    47.7 

Extra  fine  sand 8.4 

Total    99.7 

Per  cent  of 
very  fine  sand 

Light     72.3 

Heavy    26.3 

Total    98.6 

It  was  not  at  first  intended  to  weigh  the  products  of  magnetic  separation,  so  that  a 
large  amount  of  the  glauconitic  portion  was  taken  out  for  various  purposes  before  it 
was  decided  to  weigh.  From  the  weights  of  the.  other  magnetic  products,  however,  the 
weight  of  glauconite  may  be  approximated  : 

Glauconite  about  95%  of  heavy  portion  =  about  25%  of  very  fine  sand. 


140  THE  PETROGRAPHY  AND  GENESIS  OF  SEDIMENTS 

DESCRIPTION  OF  PRODUCTS 
A.  UNDEB  THE  HAND  LENS 

/.  Coarse  Band 

Contains  one  grain  of  fine  gravel.  Most  of  the  quartz  grains  are  milky,  opaque,  some 
of  them  stained  green  ;  doubtless  by  glauconlte.  A  few  of  the  grains  are  perfectly 
rounded  and  polished  like  wind-blown  sand.  The  rest  are  subrounded  or  rough  but  many 
of  them  with  the  glossy  "  solution  "  surface.  A  grain  of  clay  with  included  sand  grains 
looks  like  a  concretion  (cf.  Sample  No.  3).  Only  one  grain  of  quartz  shows  limonitic 
staining.  There  are  some  transparent,  cellular,  leaf-like  plant  fragments. 

II.  Medium  Sand 
Differs  from  the  coarse  sand  : 

(1)  In  containing  a  few  grains  of  fresh-looking,  green,  botryoidal  glauconite, 

(2)  in  containing  a  very  few  grains  of  heavy  minerals  including  a  little  mica. 

///.  Fine  Sand 

This  portion  has  a  "pepper  and  salt "  appearance  due  to  the  abundance  of  glauconlte 
mixed  with  the  quartz.  While  most  of  the  quartz  is  very  angular  there  are,  as  in  the 
preceding  portions,  still  a  number  of  very  well  rounded  grains.  Most  of  the  glauconite  is 
very  fresh  looking,  but  a  good  deal  of  it  nevertheless  shows  rounding  by  wear. 

IV.  Very  Fine  Sand 

Contains  more  glauconite  than  the  preceding,  but  is  otherwise  very  similar. 

V.  Extra  Fine  Sand 
Dark  greenish-gray,  micaceous. 


Light  greenish-gray,  micaceous. 

B.  UNDER  THE  MICKOSCOPE 
/.  Very  Fine  Sand 

(1)  Light 
Quartz  :  feldspar=90  :  10. 

The  striking  features  are : 

(a)  The  absence  of  limonitic  staining. 

(b)  The  small  amount  of  glauconite  along  cleavage  cracks  and  fissures. 

(2)  Heavy 

(a)    Attracted   at   10,000   Ohms 

As  indicated  above  this  is  principally  glauconlte.     The  minerals  identified  are  :  garnet, 
tourmaline,  deep  blue  chlorite,  staurolite,  epidote,  muscovite,  biotite,  rutile. 

(b)   Attracted  at  Full  Current 
Dominant. — Muscovite,  serpentine. 
Common. — Tourmaline,   rutile. 
Rare. — Biotite,  epidote,  enstatite,  quartz  with  rutile  inclusions. 

(c)   Non-magnetic 
Enstatite  most  common  with  much  zircon. 

//.  Extra  Fine  Sand 
The  glauconite  in  this  portion  is  in  rounded  grains. 

///.   Silt 

Here    the   glauconite    is    In    irregular    flakes.      The    product    therefore    has    a    distinct 
qualitative  though  not  a  quantitative  significance. 


MARYLAND  GEOLOGICAL  SURVEY  141 

IV.  Clay 

A  normal,  pure-looking,  blue-gray  clay  showing  under  the  microscope  few  mineral 
grains,  but  also  few  of  the  polarizing  fibrous  particles  which  appear  to  be  characteristic 
of  most  of  the  clays ;  it  is  mainly  amorphous  brown  matter. 

Summary  and  Conclusions. — This  is  a  typical,  normal  sample  of  the 
Matawan  of  this  region  and  as  such  offers  little  requiring  special  com- 
ment here.  The  condition  of  the  glauconite  in  it  seems  to  prove  that  the 
glauconite  is  primary,  so  that  this  sediment  represents  lithologic  condi- 
tions under  which  glauconite  may  be  formed.  There  has  been  very  little 
secondary  action  of  any  kind  as  is  proved  by  the  absence  of  limonitic  and 
of  glauconitic  staining,  while  the  sharpness  with  which  the  separation  of 
clay  and  sand  could  be  made  confirms  this  conclusion. 

The  seeming  argillaceous  concretions  (see  coarse  and  medium-grained 
sand)  should  be  noted.  Noteworthy,  also,  is  the  small  amount  of  carbon- 
aceous matter. 

SAMPLES  NOS.  3,  4,  5,  AND  6 

General  Summary  and  Conclusions. — These  four  samples  are  from  one 
locality  and  section  and  were  taken  in  order  to  find  what  the  analyses 
might  show  to  supplement  their  field  relations.  The  results  are  inter- 
esting enough  to  justify  a  special  discussion  here. 

Following  is  the  field  section,  beginning  at  the  top : 

FVpt 

(5)  A  capping  of  post-Cretaceous  gravel  and  diagonally  (current) 
bedded  sand. 

(4)  Very  glauconitic,  yellow,  somewhat  argillaceous  sand 2-3 

Sharp  contact  with 

(3)  Very  glauconitic,  gray,  argillaceous  sand  (Sample  6) 6 

Bed  3  seems  to  grade  into  bed  2  although  an  appearance  of  a 
sharp  contact  is  given  by  a  thin  line  of  limonitic  staining  separat- 
ing the  two  beds. 

(2)  A  light  yellow,  glauconitic  sand  containing  little  clay  in  the  upper 
part  but  growing  more  argillaceous  and  gray  towards  the  bot- 
tom ( Sample  5) 12 

About  2  feet  at  the  top  are  filled  with  tubes  ^4  inch  in  diameter, 
running  through  the  sand  in  all  directions  and  containing  very 
glauconitic  sand. 

Sharp  contact  with 

(1)  A  dark  gray,  micaceous,  glauconitic,  argillaceous  sand,  growing 
less  micaceous  and  more  glauconitic  towards  the  lower  part.  Ex- 
posed to  base  of  section 5 

(Sample  4  =  upper  micaceous  part.) 
(Sample  3  =  lower  glauconitic  part.) 
10 


142  THE  PETROGRAPHY  AND  GENESIS  OF  SEDIMENTS 

Considering  the  field  section  and  the  analyses  together  we  find  that  they 
fall  very  naturally  into  two  distinct  types. 

A.  That  represented  by  samples  3  and  4  —  bed  1 ;  micaceous  material, 
with  reworked  glauconite  and  much  carbonaceous  material. 

B.  That  represented  by  samples  5  and  6  =  beds  2  and  3;  typical 
Matawan  beds,  with  glauconite  evidently  formed  in  place. 

The  resemblance  of  type  A  to  the  Magothy  as  at  Betterton  (see 
samples  1  and  2)  is  apparent,  with  the  marked  difference,  however, 
that  there  is  here  no  rapid  alternation  vertically  in  the  character  of  the 
beds.  Without  paleontological  evidence  it  is  moreover  not  certain  that 
bed  1  here  is  not  Magothy,  though  just  as  there  was  evidently  glauconite 
formed  before  the  formation  of  the  similar  beds  of  the  Magothy  at  Better- 
ton,  so  there  is  no  apparent  reason  why  in  the  midst  of  the  glauconite 
formation  of  the  Matawan  there  should  not  be  a  facies  similar  to  the 
Magothy. 

While  the  present  state  of  our  knowledge  of  sediments  does  not  allow 
a  definite  classification  of  these  beds,  I  think  it  is  evident  that  bed  1  repre- 
sents more  of  the  river  delta  type  of  deposit  while  beds  2,  3  and  4  repre- 
sent the  more  quiet  conditions  under  which  glauconite  is  formed. 

Considering  these  two  groups  we  find  at  first  glance  a  remarkable  lack 
of  difference  in  the  relative  proportion  of  sand  and  clay  and  in  the  per- 
centage of  very  fine  sand,  but  the  striking  difference  is  in  the  distribution 
of  the  other  sizes.  Thus  in  what  are  tentatively  called  the  delta  type  there 
is  very  little  material  coarser  than  the  very  fine,  this  portion  forming  the 
maximum  and  appearing  in  the  diagrams  (figs.  C,  D,  p.  169)  with  the 
abruptness  characteristic  of  delta  and  stream  sediments  (cf.  figs.  D,  I,  J, 
p.  170) ;  at  the  same  time  the  abundant  extra  fine  gives  a  transition  to  the 
clay — a  feature  which  from  these  same  diagrams  on  p.  170  is  seen  to  belong 
more  to  this  type  of  sediments. 

Samples  5  and  6  (E,  F,  p.  169)  on  the  other  hand,  while  they  show  some 
marked  differences  from  each  other,  have  in  common  a  clear  antithesis  to 
samples  3  and  4  in  the  two  features  just  enumerated,  that  is,  there  is  a 
more  gradual  gradation  through  the  coarser  sizes  to  the  maximum  in  the 


MARYLAND  GEOLOGICAL  SURVEY  143 

very  fine,  and  a  more  sudden  drop  to  the  fine,  features  which  from  the 
diagrams  on  p.  370  are  seen  to  differentiate  open-water  sediments  from 
those  of  deltas  or  streams  (compare  figs.  A,  C,  E,  with  D,  I,  J,  p.  170) . 

Furthermore,  while  at  first  sight  the  proportion  of  heavy  minerals 
shows  no  consistent  difference  in  the  two  groups,  it  is  found  when  glau- 
conite  is  deducted  that  the  percentage  of  heavy  minerals  in  the  glauconitic 
type  is  only  2%-3%,  while  in  the  "  delta  "  type  it  is  about  8%.  Besides, 
the  deduction  of  glauconite  is  much  more  significant  in  the  glauconitic 
type,  since  here  it  is  not  an  imported  mineral.  But  while  in  its  fresh  con- 
dition glauconite  has  generally  a  specific  gravity  considerably  less  than 
2.7,  it  is  questionable  whether  the  material  in  bed  1  had  not  already 
become  partly  decomposed,  and  thus  actually  a  heavy  mineral,  before  it 
was  transported  into  bed  1.  In  sample  3,  which  is  the  portion  of  bed  1  in 
which  glauconite  is  particularly  amundant,  both  the  glauconite  itself  and 
the  ocherous  staining  of  other  minerals  support  this  belief,  as  I  have  indi- 
cated in  the  discussion  of  that  sample. 

As  to  the  history  of  the  succession  that  can  now  be  worked  out  for  this 
section  I  should  first  question  the  field  determination  of  a  sharp  contact 
between  beds  1  and  2.  On  the  contrary,  since  bed  1  is  very  argillaceous, 
and  bed  2,  while  it  grows  more  sandy  towards  the  top,  is  also  argillaceous 
at  its  base,  it  seems  more  probable  that  there  was  here  a  transition,  though 
it  may  have  been  quite  sudden. 

Then  we  have  in  bed  1  the  evidence  for  the  exposure  of  an  older  glau- 
conitic bed  to  the  atmosphere  with  partial  decomposition  of  the  glauconite 
and  ocherous  staining  of  the  other  grains.  This  bed  was  attacked  by  the 
stream  which  deposited  in  its  delta  the  material  of  bed  1,  while  through 
deepening  of  the  water  or  reduction  in  grade  of  the  supplying  stream  the 
material  gradually  grew  finer.  Ultimately  by  a  continuation  of  this  evo- 
lution the  waters  became  quiet  and  clear,  and  favorable  to  the  formation 
of  glauconite.  Under  these  circumstances  beds  2  and  3  (samples  5  and  6) 
were  formed,  but  the  conditions  controlling  were,  at  noted  above,  not  in 
all  respects  similar  for  the  two  beds.  A  glance  at  E  and  F,  p.  169,  and  com- 
parison with  the  figures  on  p.  170  show  at  once  the  essential  grouping  of 


144  THE  PETROGRAPHY  AND  GENESIS  OF  SEDIMENTS 

the  differences.  Bed  2  (sample  5,  fig.  E,  p.  169)  is  of  the  well-sorted  type 
produced  by  strong  wave  action  or  by  wind ;  bed  3  (sample  6,  fig.  F,  p.  169) 
shows  a  remarkable  resemblance  to  the  poorly-sorted  lagoonal  type  repre- 
sented in  E,  p.  170. 

The  facies  of  bed  3  (sample  6)  is  therefore  easily  recognized;  it  was 
formed  not  in  the  open  sea  but  in  a  more  enclosed  body  of  water,  a 
lagoon,  or  perhaps  an  estuary  or  an  arm  of  a  bay  like  Chesapeake  Bay  of 
to-day.  But  bed  2  (sample  5)  is  harder  to  place.  Mere  comparison  of  its 
diagram  (E,  p.  169)  with  the  diagrams  on  p.  170  shows  a  resemblance  to 
diagram  J  even  more  striking  than  that  of  F,  p.  169,  to  E,  p.  170.  This 
does  not  necessarily  mean  that  bed  2  was  wind-deposited.  Its  general  con- 
forming to  the  rest  of  the  section  with  transition  probably  at  bottom  as 
well  as  at  top  (in  any  case  a  more  argillaceous  composition  in  its  lower 
part),  and  the  fact  that  no  striking  rounding  of  the  quartz  grains  was 
noted,  are  against  this  interpretation.  The  discrepancies  can  be  adjusted 
if  it  be  assumed  that  the  difference  between  diagrams  of  wave-sorted  mate- 
rial, like  C,  p.  170,  and  wind-sorted  material  like  J,  p.  170,  is  more  funda- 
mental than  mere  difference  between  action  of  water  and  air,  and  repre- 
sents rather  the  different  effects  of  wave  and  current  action.  That  is,  a 
current  of  water  might  produce  the  same  sorting  shown  in  E,  p.  169,  as 
was  produced  in  J,  p.  170,  by  a  current  of  air. 

Theoretical  considerations  lend  support  to  this  conclusion.  For 
the  action  of  waves  consists  essentially  in  a  prolonged  working  over  of 
material  of  a  certain  maximum  degree  of  coarseness  depending  on  the 
average  uniform  conditions  under  which  material  is  supplied  to  them. 
From  this  they  tend  to  eliminate  all  the  finer  material,  producing  a 
concentration  of  the  coarsest.  Even  though  their  strength  is  constantly 
fluctuating  the  end  result  of  their  work  is  the  product  essentially  of  their 
maximum  force.  But  a  current  is  an  actively  depositing  agent,  and  while 
it  will  also  tend  to  eliminate  all  material  that  is  fine  enough  to  be  carried 
by  it,  the  sorting  it  produces  will  be  rather  the  result  of  its  mean  strength 
corresponding  to  a  certain  fineness  of  material  which  would  be  accumu- 
lated too  fast  to  be  accessible  for  reworking  by  its  maximum  strength. 
Hence  the  coarsest  material  brought  in  during  periods  of  maximum 


MARYLAND  GEOLOGICAL  SURVEY  145 

strength  would  represent  a  minor  admixture  to  a  larger  quantity  of  its 
average  size.  In  this  way  would  result  the  difference  between  marine  and 
wind  sediments  shown  by  diagrams  C  and  J,  p.  170,  in  that  in  the  marine 
deposits,  which  are  essentially  the  products  of  wave  action,  the  next  largest 
quantity  after  the  maximum  is  in  the  next  finest  material,  while  in  dune 
sands,  which  are  essentially  current-deposits,  it  is  in  the  next  coarsest. 
That  is  to  say,  in  wave-worked  material  there  would  be  an  admixture  of 
finer  material  which  had  escaped  the  maximum  wave  strength,  while  in 
current-deposits  the  products  of  their  greatest  strength  would  appear  as 
the  admixture  and  the  finer  material  produced  by  their  average  strength 
would  survive  as  the  maximum. 

That  some  sorting  action  and  not  the  advent  of  coarser  material  is 
responsible  for  the  presence  of  a  smaller  amount  of  very  fine  sand  in  bed  3 
(sample  6,  F,  p.  169)  than  in  bed  2  (sample  5,  E,  p.  169)  appears  from 
the  fact  that  there  is  actually  more  of  coarse,  medium,  and  fine  sand 
together  in  the  argillaceous  sample  6  than  in  the  sandy  sample  5.  It  may 
still  be;,  in  view  of  our  imperfect  knowledge  of  the  mechanical  composi- 
tion of  sediments,  that  in  spite  of  the  divergence  of  sample  5  from  typical 
wave-worked  sediments  it  is  nevertheless  the  product  of  deposition  in 
more  open  water,  perhaps  as  a  result  of  the  deepening  suggested  above, 
and  that  as  deposition  continued,  or  possibly  uplift  of  the  region  replaced 
subsidence,  the  area  in  which  this  section  was  deposited  became  cut  off  as 
a  lagoon  or  estuary.  But  the  interpretation  that  the  difference  is  clue  to  a 
local  current  which  passed  over  the  area  when  the  lower  bed  (bed  2)  was 
being  deposited,  but  disappeared  before  the  deposition  of  the  upper  bed 
(bed  3),  seems  the  more  probable. 

The  position  of  the  line  of  limonite  staining  between  beds  2  and  3 
is  probably  determined  by  distance  from  the  surface  and  porosity  com- 
bined. Such  lines  are  common  throughout  the  region  and  by  their  wavy 
form  and  lack  of  relation  to  the  lithology  show  that  they  are  secondary 
and  formed  by  circulating  ground  waters. 

Bed  4  may  represent  shallowing  of  the  water,  but  as  it  is  at  the  top  of 
the  section  its  sandy  yellow  appearance  is  more  probably  due  to  alteration, 
so  that  in  the  absence  of  an  analysis  nothing  definite  can  be  said  about  it* 


146  THE  PETROGRAPHY  AND  GENESIS  OF  SEDIMENTS 

SAMPLE  NO.  7    (FIG.  G,  p.  169) 
Serial  number  :  15. 
Field  number  :  3-9-12-1911. 
Formation  :  Matawan. 

Locality  :  Camp  Fox,  Chesapeake  and  Delaware  Canal. 
Appearance  :  Friable,  sandy,  gray-white  marl,  speckled  with  glauconito. 

MECHANICAL  ANALYSIS 

Sample    8-404  8m- 

Treated  with  dilute  HC1  to  dissolve  lime. 

Per  cent  of 
sample 

Lime-free  residue 80.2 

Lime  (by  difference) 19.8 

Total    100.0 

Per  cent  of 
lime-free  residue 

Sands    87.8 

Silt    0.9 

Clay  (by  difference)    11.3 

Total    100.0 

Per  cent  of 
total  sands 

Coarse  sand   0.2 

Medium  sand    16.2 

Fine  sand   60.6 

Very  fine  sand 20.0 

Extra  fine  sand   ,  .     2.8 


Total 


Per  cent  of 
very  flue  sand 

Light     57.3 

Heavy    42.2 

Total     99.5 

MAGNETIC  SEPARATION 

Per  cent  of 
total  heavies 

Attracted  at  2000  ohms  (glauconite) 86.0    =36.2%  of  very  fine 

Attracted  at  full  current 7.5~| 

Non-magnetic     0.4  L_       6%  of  very  fine 

Magnetite    3.0J 

Total 96.9 

Per  cent  of 
2000-ohms 
portion. 

Attracted  at  2000  ohms,  S.  G.>  3.002 13.9 

Attracted  at  2000  ohms,  S.  G.<3.002   (glauconite)1...   86.1  =  74.0%  of  heavy  =  31.2%  of 

very  fine 

Total    100.0 

*A  minimum  value  for  glauconite  In  this  portion,  since  some  glauconite  came  down 
with  the  part  heavier  than  3.002.  There  are.  on  the  other  hand,  some  heavy  minerals 
especially  mica  in  the  part  that  flloated  at  3.002  though  their  weight  is  doubtless  less 
than  that  of  the  glauconite  that  settled.  Good  approximations  are  probably  : 

Glauconite  80%  of  heavyr=35%  of  very  fine, 
which  leaves  actual  heavy  minerals  about  7%  of  the  very  fine. 


MARYLAND  GEOLOGICAL  SURVEY  147 

DESCRIPTION  OP  THE  PRODUCTS 

A.  UNDER  THE  HAND  LENS 
/.  Lime- free  Residue 

This  separates  in  water  into  two  very  distinct  parts : 

(1)  Very  glauconitic  clear  sands. 

(2)  Dark  brown  clay  (probably  with  considerable  limonite)  which  floats  on  top. 

77.  Coarse  Sand 

Eight  grains  of  quartz  with  glossy,  pitted  surfaces ;  one  of  them  is  stained  green  ;  one 
is  sugary  and  stained  brown.  Some  leaf  fragments. 

III.  Medium  Sand 

Glossy,  angular  quartz ;  some  sugary  grains  stained  brown  as  in  II ;  almost  no  grains 
stained  green.  Very  fresh  botryoidal  glauconite ;  some  rounded  grains  of  glauconite. 

IV.  Fine  Sand 

Much  of  the  glauconite  is  rounded  and  more  than  in  III  is  faded  yellowish  ;  otherwise 
the  glauconite  is  as  in  III.  There  is  very  little  mica. 

V.  Very  Fine  Sand 

The  glauconite  is  almost  all  rounded,  much  of  it  weathered  yellowish.  The  grains  of 
quartz  are  all  angular. 

VI.  Extra  Fine  Sand 
General  appearance  green.     The  glauconite  is  half  yellowish,  half  fresh,  blue-green. 

B.  UNDER  THE  MICROSCOPE 

/.   Very  Fine  Sand 

(1)    Light 

Quartz  :  feldspar  =  90  :  10. 

The  determination  of  the  proportion  of  feldspars  present  is  made  difficult  by  the 
presence  of  minerals  in  various  stages  of  decomposition,  towards  a  mass  with  complex 
aggregate  polarization,  which  may  be  derived  from  feldspars.  Difficulties  are  also  afforded 
by  cloudy  grains  which  may  be  quartzite.  Most  of  the  feldspars  are  much  weathered.  A 
grain  of  plagioclase  was  noted.  There  is  much  irregular  glauconitic  staining  of  grains, 
and  glauconite  in  thick  seams  along  cleavage  cracks.  Many  grains  of  glauconite  are 
present. 

(2)    Heavy 

(a)  Attracted  at  2000  Ohms,  S.  G.> 3.002 

More  than  half  glauconite.  Magnetite  largest  part  of  remainder,  many  of  the  grains 
well  rounded.  Red  garnet  a  little  less  common  than  magnetite.  Epidote  and  staurolite 
rather  common.  Some  chlorite.  Green  zircon  (?). 

(b)   Attracted  at  2000  Ohms,  S.  G.< 3.002 

Almost  pure  glauconite,  in  well  rounded  or  botryoidal  grains,  opaque  to  slightly  trans- 
lucent, free  from  coarse-granular  inclusions.  The  botryoidal  grains  are  very  scarce. 
There  is,  in  addition,  a  very  little  muscovite  and  quartz. 

(c)  Attracted  at  Full  Current 

Tourmaline,  rutile,  augite,  biotite,  muscovite,  green  zircon,  chlorite,  glauconite.  The 
glauconite  in  this  portion  is  in  rough,  irregular  grains,  cloudy,  to  opaque,  mostly  full 
of  black  mineral  grains.  Many  of  the  grains  that  look  like  chlorite  are  found  to  have 
undulatory  to  aggregate  polarization  indicating  that  they  are  in  a  transition  stage  from 
or  to  chlorite.  In  view  of  the  fact  that  glauconite  is  itself  believed  to  be  one  of  the 
chlorites  this  may  be  of  significance  for  the  formation  of  glauconite.  Two  small,  remark- 
ably spherical  grains  of  quartz  are  noteworthy. 

(d)    Non-magnetic 

Most  common  enstatite,  zircon,  augite,  hornblende,  apatite,  rutile,  andalusite  ( ?).  The 
good  preservation  of  the  crystal  form  of  the  rutile  Is  striking. 


148  THE  PETROGRAPHY  AND  GENESIS  OF  SEDIMENTS 

(e)    Magnetite 
Very  angular,  with  a  few  rounded  grains.     Much  glauconite  included.     Some  garnet. 

II.  Extra  Fine  Sand 
Largely  glauconite  in  irregular  grains. 

///.  Silt 
Nothing  of  interest.     Mineral  grains,  much  mica,  glauconite.     Very  few  limonite  flakes. 

Summary  and  Conclusions.— This  sample,  which  may  be  considered 
typical  of  the  facies  of  the  Matawan  in  this  neighborhood,  is  interesting, 
first  of  all  for  its  marly  character,  that  is  for  the  combination  in  it  of  clay 
and  high  lime  content  with  glauconite.  With  the  high  lime  content  goes 
a  great  richness  in  fossils.  I  can  see  no  reason  for  considering  this  differ- 
ence other  than  primary,  since  there  is  no  factor  apparent  that  would  pre- 
serve the  lime  here  more  than  in  other  occurrences.  Of  course  it  is 
assumed  that  foraminifera  originally  occurred  in  all  the  primary  glau- 
conitic  rocks,  but  their  shells  would  form  merely  a  thin  coating  on  the 
individual  glauconitic  grains,  not  a  calcareous  argillaceous  mass  through 
which  the  glauconite  might  be  distributed.  It  is,  therefore,  fair  to  assume 
that  the  bed  was  formed  under  conditions  unusually  favorable  to  the  life 
of  neritic  shell  bearing  forms. 

The  diagram  for  the  sample  (K,  p.  169)  is  that  of  a  rather  normal  open- 
water  off-shore  sediment,  with  sorting,  however,  less  perfect  than  in 
marine  off-shore  deposits. 

In  the  mineral  composition  there  is  noteworthy  the  occurrence  of  sev- 
eral minerals  scarce  or  very  rare  in  other  samples,  especially  hornblende, 
augite,  apatite,  and  andalusite.  The  unusually  good  preservation  of  the 
crystal  form  of  rutile  indicates  its  derivation  from  nearby. 

The  general  fresh  condition  of  the  glauconite  is  characteristic  for  the 
sample.  In  view  of  this  fact  it  does  not  seem  probable  that  the  irregular 
grains  of  glauconite  with  inclusions  represent  a  decomposition  product, 
for  in  that  case  some  intermediate  stages  would  be  expected.  More  prob- 
ably, therefore,  they  are  a  distinct  type  of  glauconitic  product.  Their 
form  and  ocurrence  suggest  analogies  with  the  limonitic  flakes  in  many 
samples,  which  are  probably  mainly  small  encrustations  loosened  from 
the  grains  on  which  they  occur.  In  the  same  way  these  would  be  loosened 
flakes  of  glauconite  encrustations,  such  as  are  found  on  the  surface  and  in 


MARYLAND  GEOLOGICAL  SURVEY  149 

cracks  of  many  quartz  and  feldspar  grains  in  this  and  other  samples. 
While  the  botryoidal  grains  of  glauconite  were  presumably  formed  in  the 
shells  of  foraminifera,  these  encrustations  and  stains  must  have  been 
formed  unenclosed  in  the  midst  of  the  sediment.  Though  the  manner  of 
their  formation  is  not  yet  clear  this  difference  in  the  conditions  under 
which  they  developed  may  well  account  for  their  different  appearance. 

Concerning  the  complex  chloritic  grains,  also  in  the  full-current 
product,  I  have  no  interpretation  to  suggest,  but  merely  draw  attention 
to  them  again  here. 

SAMPLE  NO.  8    (FIG.  H,  p.  169) 
Serial   number  :   16. 
Field  number  :  5-9-12-1911. 
Formation  :  Matawan  or  Monmouth. 
Locality  :  Camp  Fox,  Chesapeake  and  Delaware  Canal. 

Appearance  :   Fine-grained,  dark-green,  speckled  sand,  considerably  weathered  and  stained 
with  limonite. 

MECHANICAL  ANALYSIS 
Sample    7.700  gm. 

Per  cent  of 
sample 

Sands    88.8 

Silt    0.6 

Clay    11.1 

Total     100.5 

Per  cent  of 
total  sands 

Coarse  sand    0.5 

Medium   sand   27.2 

Fine  sand   42.8 

Very  fine  sand   26.3 

Extra  fine  sand 2.9 

Total     99.7 

Per  cent  of 
very  fine  sand 

Light     63.2 

Heavy    36.5 

Total    99.7 

MAGNETIC  SEPARATION  Per  cent  of 

total  heavies 

Attracted  at  1500  ohms 90.5 

Attracted  at  full  current 4.4 

Non-magnetic     0.2 

Magnetite    1.8 

Total     96.9 

Per  cent  of 
1500-ohms 
portion 

Attracted  at  1500  ohms,  S.  G.  >  3.002 6.2 

Attracted  at  1500  ohms,  S.  G.<3.002   (glauconite)...    94.8  =  85.8%  of  heavy  =  31.3%  of 

very  fine 

Total    .  101.0 


150  THE  PETROGRAPHY  AND  GENESIS  OF  SEDIMENTS 

DESCRIPTION  OF  PRODI*  "IS 

A.  UNDER  THE  HAND  LENS 

/.  Coarse  Sand 

Quartz  grains  so  strongly  pitted  that  their  original  form  is  obscured.  Many  of  them 
are  stained  yellow.  Besides  the  quartz  there  are  brown,  opaque,  limonitic  grains.  One 
of  these  has  the  characteristic  form  of  an  agglomerated  glauconite  grain.  There  are 
two  little  concretions  of  sand,  one  In  a  dark  blackish  matrix,  the  other  in  a  yellow, 
limonitic  cement  like  the  concretions  in  sample.  3. 

//.  Medium  Sand 

Yellowish-green,  specked  with  dark  glauconite.  The  quartz  is  angular.  Glauconite 
botryoidal.  Smooth  reddish-brown  grains  of  which  one  or  two  were  seen  in  the  coarse 
sand  are  more  common  here.  Some  of  them  have  a  conchoidal  fracture  like  limestone, 
and  the  fresh  surface  is  pinkish-white.  Others,  probably  partly  decomposed,  are  brittle 
and  pale  yellow  inside.  They  dissolve  with  effervescence  in  cold  dilute  hydrochloric  acid. 
They  are  therefore  probably  either  siderite,  or  calcite  or  aragonite  stained  by  limonite. 
Their  smooth  rounded  form  and  glossy  surface  suggest  their  origin  in  connection  with 
some  organic  process. 

///.  Fine  Sand 

Like  II  except  that  there  appears  to  be  somewhat  more  glauconite  and  that  most  of  the 
glauconite  is  in  rounded  grains. 

IV.  Very  Fine  Sand 
Like  preceding  but  much  of  the  glauconite  turned  yellow. 

B.  UNDER  THE  MICROSCOPE 

/.  Light 

Quartz  :  feldspar  =  90  :  10. 

General  appearance  greenish  with  some  grains  of  glauconite  and  some  limonitic  stain. 
There  is  much  glauconite  along  the  cleavage  of  feldspars  and  in  irregular  staining 
patches  on  the  outside  of  the  grains.  Some  of  the  glauconite  grains  seem  to  show 
almost  their  original  botryoidal  form. 

//.  Heavy 

(1)  Attracted  at  1500  Ohms,  S.  G.  >  3.002 

Dominant. — Magnetite,  garnet  (red  and  colorless),  epidote,  staurolite. 
Rarer.— Tourmaline,  chlorite,  chlorltoid  (1  grain). 

(2)  Attracted  at  1500  Ohms,  S.  G.<3.002 

Practically  pure  glauconite.  Opaque  and  densely  clouded  grains  with  a  yellowish 
tinge.  They  do  not  show  coarse  granular  inclusions  only  a  fine  disseminated  powder 
responsible,  at  least  in  part,  for  the  cloudiness. 

(3)  Attracted  at  Full  Current 

Under  the  hand  lens  much  rusted  glauconite  and  other  rust-colored  minerals.  Chlorite, 
muscovite,  blotite,  tourmaline,  andalusite,  augite,  apatite,  rutile,  enstatite,  zircon, 
kyanite,  aragonite.  Particularly  characteristic  are  two  types  of  grains  to  which  the 
brown  color  of  the  portion  is  largely  due.  These  are : 

(a)  A  brown  granular,  non-polarizing  grain  which  looks  like  what  I  have  been  calling 
limonite  but  which  dissolves  completely  in  dilute  acid,  with  strong  effervescence. 

(b)  A  brown,   translucent   mineral   occurring  in   irregular  forms  but  also   in   parallel 
sided   (prismatic)    grains.     The.  grains  of  irregular  shape  have  imperfect,  more  or  less 
undulatory  extinction,  but  that  of  the  prismatic  grains  is  generally  perfect  and  parallel. 
These  grains  also  dissolve  with  effervescence  in  dilute  acid,  but  seemingly  not  always 
completely,  leaving  a  skeleton  or  nucleus. 


MARYLAND  GEOLOGICAL  SURVEY  151 

The  only  explanation  I  have  for  (b)  Is  that  It  is  aragonlte  stained  with  Hmonite.  The 
form  and  undulatory  extinction  of  some  of  the  fragments  of  this  type  suggest  that  they 
are  parts  of  the  shells  of  some  animal — (a)  Is  probably  something  similar,  but  I  cannot 
explain  its  non-polarizing.  The  matter  requires  further  study.  Most  of  the  flakes  of 
mica  and  grains  of  decomposed  minerals  in  this  portion  are  stained  green. 

(4)    Non-magnetic 

Dominant. — Zircon,  enstatite,  apatite,  In  about  equal  amounts. 
Rare. — Kyanlte,  rutile. 

(5)  Magnetite 

Almost  all  in  angular  grains.  Contains,  besides,  much  slightly  cloudy,  yellowish-green 
glauconite.  Some  muscovite  and  garnet. 

///.  Extra  Fine  Sand 

General  appearance  drab  olive-green.  Light  minerals  and  glauconite  in  about  equal 
proportions,  with  of  course  some  rare  minerals.  The  glauconite  is  both  in  rounded 
grains  and  in  irregular  fragments.  There  are  some  limonitic  flakes. 

IV.  Silt 

Limonitic  flakes  are  prominent  In  this  portion.  There  is  less  glauconite  than  in  the 
extra  fine-grained. 

V.  Clay 

General  appearance  faint  yellowish-gray,  with  not  as  much  limonitic  material  as 
might  be  expected  from  the  character  of  the  rock.  There  is  a  considerable  amount  of  the 
fibrous  material  which  has  been  found  characteristic  of  the  clays. 

SAMPLES  NOS.  7  AND  8 

General  Summary  and  Conclusions. — The  significance  of  sample  8  is 
largely  in  its  relation  to  sample  7,  so  that  it  must  first  of  all  be  con- 
sidered in  connection  with  this. 

In  the  field  the  upper  part  of  the  marly  glauconite  sand  from  which 
sample  7  is  taken  was  found  to  be  full  of  pycnodont  shells  much  worn, 
bored,  and  sometimes  broken.  This  condition  seems  to  indicate  a  period 
of  exposure  in  shallow  coastal  water.  Together  with  the  sharp  contact 
between  this  bed  and  the  overlying,  it  proves  a  disconformity,  at  least 
locally. 

The  most  striking  fact  about  their  relations  is  the  almost  perfect  simi- 
larity in  every  respect  except  the  lime  content. 

The  sands  in  the  upper  bed  (sample  7,  fig.  L,  p.  169)  are  a  little 
coarser  and  a  little  less  perfectly  sorted,  but  in  the  proportions  of  sand 
and  clay,  the  general  relation  of  the  different  sizes  and  the  mineral  content 
there  is  remarkable  agreement.  This  extends  even  to  the  proportion  of 
glauconite,  which  is  almost  exactly  the  same  in  the  two  beds.  The  only 


152  THE  PETROGIUPHY  AND  GENESIS  OF  SEDIMENTS 

difference  is  a  secondary  one  that  might  be  expected  from  the  loose  texture 
of  the  upper  bed  as  against  the  compactness  of  the  lower — namely,  more 
limonitic  matter  in  the  upper.  But  it  is  very  interesting  to  note  that  the 
glauconitic  staining  of  mineral  grains  is  not  one  of  these  secondary  dif- 
ferences; nor  the  apparently  altered  opaque  condition  of  the  glauconite; 
which  would  thus  seem  to  have  been  produced  before  the  beds  were 
emerged. 

The  two  beds  are  thus  so  intimately  related  that  if  it  were  not  for  the 
accumulation  of  oysters  in  the  top  of  the  lower  bed  one  would  be  led  to 
assume  continuous  deposition.  The  essential  difference  is  in  the  presence 
of  abundant  shells  in  the  lower  bed.  It  may  be  that  the  somewhat  less 
agitated  condition  of  the  water  in  which  the  upper  bed  was  deposited 
produced  enough  difference  to  make  the  area  relatively  unfavorable  for 
the  animal  life  which  had  abounded  at  the  time  the  lower  bed  was  formed. 
In  any  case  the  change  appears  to  have  been  a  subtle  one. 

SAMPLE  NO.  9    (FIG.  I,  p.  169) 
Serial  number  :   19. 
Field  number  :  17-9-28-1911. 
Formation  :  Matawan. 

Locality  :  Grove  Point,  mouth  of  Sassafras  River. 

Appearance  :  Dark  blackish-gray,  fine-grained,  micaceous,  argillaceous  sand  with  some 
scattered  pebbles  of  fine-grained  white  quartz  too  scarce  to  have  been  caught  in 
analysis. 

MECHANICAL  ANALYSIS 
Sample    10.780  gm. 

Per  cent  of 
sample 

Sands    68.5 

Silt    2.1 

Clay     28.2 

Total    98.8 

Per  cent 'of 
total  sands 

Coarse  sand 0.1 

Medium  sand 0.4 

Fine  sand 0.5 

Very  fine  sand 45.1 

Extra  fine  sand   53.0 

Total . .    99.1 

Per  cent  of 
very  fine  sand 

Light    91.4 

Heavy     5.6 

Total    .  . .   97.0 


MARYLAND  GEOLOGICAL  SURVEY  153 

DESCRIPTION  OF  PRODUCTS 

A.  UNDER  THE  HAND  LENS 

/.  Coarse  Sand 

Nine  grains  of  milky  quartz,  some  very  rough,  others  rounded  but  strongly  coroded. 
Several  black  carbonaceous  flakes. 

//.  Medium  Sand 

Much  like  the  coarse  sand,  with  some  glossy  quartz  in  small  angular  grains,  with 
more  well  rounded  grains  than  the  coarse  sand,  some  mica,  and  much  black  carbonaceous 
matter  mainly  fragments  of  wood. 

///.  Fine  Sand 

Very  much  white  mica  and  some  chlorite.  Most  of  the  quartz  is  sharply  angular  but 
there  are  still  some  rounded  grains.  There  are  a  few  grains  of  heavy  minerals,  zircon, 
garnet,  etc.  Very  much  black  carbonaceous  matter  as  above. 

IT.  Very  Fine  Sand 

Silver-gray  with  much  mica  and  much  fine  carbonaceous  matter.  It  is  darker  than  the 
extra  fine  sand  which  apparently  contains  little  carbonaceous  matter. 

B.  UNDER  THE  MICROSCOPE 

I.  Very  Fine  Sand 
(1)    Light 

Quartz  :  feldspar =95+   :  5  —  . 

It  is  hard  to  count  the  feldspars  in  this  sample  on  account  of  the  aggregate  polariza- 
tion of  many  grains  which  probably  are  decomposing  feldspars  but  which  cannot  be 
identified.  However,  this  should  be  regarded  as  an  essential  character  of  the  rock  and 
with  the  low  percentage  of  feldspar  shows  that  the  decay  of  the  feldspars  had  advanced 
far  in  this  sample. 

There  is  a  great  variety  of  feldspars  present  including  some  plagioclase. 

The  material  is  characterized  by  a  dirty  yellowish  staining  of  the  grains  neither 
ocherous  nor  glauconitic  but  in  a  very  few  cases  looking  like  remnants  of  a  glauconitic 
stain.  There  are  a  few  chloritic  grains  which,  however,  show  aggregate,  incomplete,  or 
undulatory  polarization,  and  some  very  pale  greenish-yellow  without  noticeable  bire- 
fringence. 

There  is  considerable  muscovite.     No  glauconite  was  found. 

(2)    Heavy » 
(a)    Magnetic 

Dominantly  muscovite  with  abundant  chlorite  and  biotite.  A  very  little  garnet  and 
tourmaline  were  found. 

(b)    Non-magnetic 
Zircon. 

//.  Extra  Fine  Sand 

Fine  grayish-white  sand.  Quite  pure,  unstained  quartz  and  feldspar  with  some 
scattered  carbon  and  a  few  grains  of  green  chlorite  in  evidence. 

///.  Silt 

Darker  gray,  more  micaceous  than  II.  Under  the  microscope  like  the  extra  fine  sand 
with  more  carbonaceous  matter  and  more  mica.  There  are  many  of  the  pale  yellow 
chloritic  grains  that  were  observed  in  the  very  fine  light  portion. 

IV.  Clay 

Pure  blue-gray.  Unusually  rich  in  the  fibrous,  dirty-colored,  polarizing  material  found 
so  characteristic  of  the  clays. 

1  This  was  the  first  sample  examined  for  minerals  so  that  the  identification  is  probably 
not  complete. 


154  THE  PETROGRAPHY  AND  GENESIS  OF  SEDIMENTS 

Summary  and  Conclusion. — The  prominence  of  fine-grained  material 
in  the  sample  and  the  abundant  mica  and  carbonaceous  matter  recall  the 
Magothy  formation  of  this  region,  but  it  differs  from  the  Magothy  in  the 
field  by  occurring  in  massive  beds,  while  the  Magothy  is  thin-bedded  or 
laminated.  Moreover,  there  are  marked  differences  in  the  composition  of 
the  material.  Its  diagram  (G,  p.  1G9)  is  peculiar  in  that  while  it  shows 
almost  only  fine  material  the  nearly  equal  proportion  of  the  different  sizes 
is  striking.  The  abrupt  rise  of  the  "  curve  "  on  the  right  is  a  character,  as 
already  noted,  of  stream  sediments,  but  the  stream  sediments  shown  in 
diagram  M,  p.  170,  do  not  show  so  large  an  admixture  of  clay  to  sands.  In 
the  study  of  this  bed  in  the  field  a  peculiar  mottled  effect  of  light  and 
dark-gray  portions,  which  on  close  examination  were  found  generally  to 
consist  of  cylindrical  tubes  of  the  light  sand  running  at  random  in  more 
or  less  vertical  directions  through  a  matrix  of  the  dark  sand,  was  noted. 
They  did  not  resemble  worn  tubes  which  are  generally  solid  cylinders,  not, 
like  these,  hollow  cylinders  filled  with  the  dark  material  that  surrounds 
them.  The  interpretation  which  suggested  itself  at  the  time  was  that 
the  sand  had  been  deposited  in  the  midst  of  reeds  which  after  their  decay 
had  been  replaced  by  clay  but  had  bleached  the  sand  around  them.  I  think 
this  clue  leads  to  a  diagram  which  while  not  exactly  like  G,  p.  169,  yet 
explains  some  of  its  anomalies.  On  p.  170  are  two  diagrams,  G  and  H,  of 
materials  from  the  same  general  lithologic  belt  in  the  Lagoon  of  Thau,  but 
H  representing  sediment  deposited  in  a  portion  of  the  lagoon  overgrown 
with  water  plants.  The  effect  of  such  a  tangle  of  plants  would  naturally  be 
to  produce  less  perfect  sorting,  and  this  is  what  we  see  in  comparing  dia- 
grams G  and  H,  p.  170,  the  extra  fine  portion  having  been  increased  at  the 
expense  of  the  clay  but  without  an  increase,  even  with  a  slight  decrease, 
in  the  relative  amounts  of  the  portions  coarser  than  extra  fine.  This 
low  proportion  of  these  coarser  sizes  would  naturally  result  from  their 
interception  in  the  same  way  by  the  nearer-shore  portions  of  the  same 
plant  areas.  As  a  result  of  these  processes  then,  a  diagram  like  I,  p.  169, 
though  of  the  general  lagoonal  type,  comes  to  resemble  more  specifically 
diagram  H,  p.  170,  the  extra  fine  sand  and  a  part  of  the  clay  having  been 


MARYLAND  GEOLOGICAL  SURVEY  155 

increased  by  the  holding  action  of  a  plant  tangle  so  as  to  equalize  their 
amount  more  with  that  of  the  very  fine  sand. 

Combining  this  conclusion  with  the  stream  character  indicated  by  the 
sharp  rise  of  the  "  curve  "  on  the  left  we  have  here  a  sediment  deposited 
where  a  stream  discharged  into  or  flowed  through  the  midst  of  plants  in 
some  small  quiet  body  of  water.  Eegarding  the  grains  of  quartz  in  the 
coarser  sizes  it  should  be  borne  in  mind,  not  only  for  this  sample  but  for 
all  others,  that  there  is  always  the  possibility,  especially  in  near-shore 
deposits  such  as  these,  that  they  have  been  brought  in  by  wind.  Thoulet  * 
has  shown  the  transporting  power  of  wind,  a  strong  gale  (13m.  per  sec.) 
being  able  to  carry  grains  over  1  mm.  in  diameter,  and,  while  these  theo- 
retical deductions  are  somewhat  invalidated  by  Udden's 2  observations  on 
wind  deposits  and  his  theoretical  deduction  that  the  effective  force  of  the 
wind  is  only  that  which  survives  the  friction  of  the  earth's  surface  (prob- 
ably never  exceeding  3  miles  an  hour),  it  is  yet  indicated  by  observation 3 
as  well  as  theory  that  an  occasional  coarse  grain  is  brought  in  by  winds. 
This  agent  therefore  may  well  be  accountable  for  the  few  grains  even  of 
the  coarsest  size  found  in  this  sample;  that  a  current  which  transports 
material  so  very  predominantly  of  the  finest  sizes  should  ever  bring  in 
these  few  scattered  coarse  grains  seems  very  improbable,  while  it  is  reason- 
able to  believe  that  an  occasional  strong  wind  would  be  quite  able  to 
supply  them. 

The  rounding  of  these  grains  which,  as  noted  above,  is  a  marked 
characteristic  of  many  of  the  grains  of  the  fine  sand  is  a  feature  more 
common  in  wind-blown  than  in  water-transported  sand,  and  therefore  also 
lends  support  to  this  conclusion. 

There  is  another  feature  of  the  sample,  however,  which  is  perhaps  of 
even  greater  stratigraphic  interest  than  the  evidence  of  the  conditions  of 
its  deposition.  That  is,  the  indications  of  weathering  which  its  material 
bears,  and  the  absence  of  glauconite.  Since  other  deposits  of  this  type 

1  Thoulet,  J.,  Analyse  d'une  poussi&re  6olienne  de  Monaco,  etc.   Annales  de 
1'Inst.  Oceanograph.  Tome  iii,  Fasc.  2,  Paris,  1911,  8  pp. 

2  Udden,  J.  A.,  Op.  cit. 

3  See  Thoulet's  observations,  in  the  paper  just  cited,  on  sediments  off  the 
Azores  supposed  to  have  been  brought  by  wind  from  the  Desert  of  Sahara. 


156  THE  PETROGRAPHY  AND  GENESIS  OF  SEDIMENTS 

have  been  studied  and  the  material  in  them  not  found  so  weathered  it  is 
justifiable  to  conclude  that  the  sands  of  this  sample  were  weathered 
before  they  entered  the  bed.  This  would  presumably  be  the  interval  cor- 
responding to  a  disconformity  between  the  Magothy  and  Matawan  during 
which  sedimentary  beds  from  which  this  material  was  derived  were 
exposed  to  atmospheric  weathering.  The  absence  of  glauconite  also  tends 
to  confirm  this  belief,  for  while  the  beds  contributing  it  to  the  Magothy 
(in  which  it  is  all  reworked)  might  have  just  become  exhausted  with  the 
closing  of  the  Magothy,  it  is  very  improbable  that  the  two  phenomena 
would  so  closely  agree  in  time,  and  much  more  probable  that  there  had 
been  a  considerable  interval  during  which  either  the  glauconitic  beds  were 
completely  eroded,  or  the  glauconite  entirely  decomposed. 

SAMPLE  NO.  10   (FIG.  J,  p.  169) 

Serial  number  :  4. 

Field  number  :  4-9-28-1911. 

Formation  :  Matawan  just  below  the  contact  with  the  Monmouth,  or  basal  Monmouth. 

Locality  :  Sassafras  River. 

Appearance  :  A  greenish-yellow,  lumpy,  crumbly  sand,  full  of  limonite  spots  and  with 
some  tinges  of  a  lavender-brown  clay.  Under  the  hand  lens  it  shows  rather  angular 
quartz  sand  with  small,  rusty  grains  of  glauconite ;  and  throughout  the  mass,  but 
seemingly  related  to  the  glauconite,  an  epidote-colored  stain.  On  a  freshly-broken 
surface  the  lavender-brown  argillaceous  matter  is  evident. 

MECHANICAL  ANALYSIS 
Sample  for  gravel 1 205.075  gm. 

Per  cent  of 
sample 

Medium  gravel    0.4 

Fine  gravel    1.6 

Sands    98.0 

Total    100.0  * 

Sample  for  sands  and  clay 10.236  gm. 

Per  cent  of 
sample 

Sands  *    62.1 

Silt    3.7 

Clay    24.1 

Total    89.9 

Per  cent  of 
total  sands 

Coarse  sand 1.1 

Medium  sand 37.6 

Fine   sand    43.6 

Very  fine  sand 14.2 

Extra  fine  sand ,  .      3.5 


.  100.0  : 


1  By  summation  of  parts. 

1  Total  sands  by  summation  of  parts. 


MARYLAND  GEOLOGICAL  SURVEY  15? 


Per  cent  of 
very  fine  sand 

Light     94.6 

Heavy    5.4 

Total    100.0 

DESCRIPTION  OF  PRODUCTS 

A.  UNDER  THE  HAND  LENS 

/.  Coarse  Sand 

Grains  of  glassy  quartz  and  some  opaque,  subrounded  but  showing  a  glossy,  pitted 
surface  as  if  solution  had  acted  on  them.  The  opaque  grains,  which  are  probably  a 
saccharoidal  quartz  of  quartzitic  origin,  are  penetrated  by  an  ocherous  stain  of  which 
there  are  traces  on  some  of  the  other  grains.  There  are  almost  no  grains  that  look  as  if 
they  had  been  well  rounded  before  solution  acted  on  them. 

//.  Medium  Sand 

Much  like  the  coarse,  but  there  seems  to  be  a  somewhat  larger  number  of  rounded 
grains  in  it. 

777.  Fine  Sand 
Like  preceding. 

B.  UNDEE  THE  MICROSCOPE 

/.  Very  Fine 

(1)  Light 
Quartz  :  feldspar=90  :  10. 

The  feldspars  are  striking  for  the  predominance  of  fresh  grains  (probably  mostly 
sanidine)  among  them.  Feldspars  showing  the  characteristic  kaolonization  along 
cleavage  cracks  are  very  rare.  Some  were  observed  that  had  small  bands  of  glauconite 
arranged  along  cleavage  cracks. 

(2)  Heavy 

Among  the  heavy  minerals  glauconite  generally  in  weathered,  brown,  opaque  grains 
is  the  most  common. 

Common. — Magnetite  unusually  abundant ;  garnet  very  common  ;  epidote. 

Rarer. — Tourmaline,  chlorite,  staurolite,  rutile,  zircon,  enstatite,  kyanite.  Striking 
in  this  rock  are  the  varieties  of  zircon  ;  besides  the  usual  colorless  to  pale  hyacinth  there 
are  grass-green  and  smoke-brown  zircons. 

77  Silt 

The  silt  in  this  case  differs  markedly  from  the  very  fine  sand  in  that  much  of  the 
limonite  present  has  gone  into  the  silt,  while  the  very  fine  sand  is  made  up  mostly  of 
fresh  primary  mineral  grains. 

777  Clay 

The  product  called  clay  is  here,  as  in  all  samples  in  which  much  limonite  has  been 
formed  by  weathering,  a  very  impure  product  containing,  in  addition  to  true  primary 
matter,  much  of  this  secondary  limonite. 

Summary  and  Conclusions. — The  principal  features  of  this  sample  are : 
(1)  The  prominence  of  the  coarser  sizes  of  sand  and  the  marked  lack 
of  sorting.    The  diagram  (I,  p.  169)  is  distinctly  of  the  lagoonal  type  (cf. 
A,  p.  169,  and  E,  p.  170)  and  therefore  requires  no  special  comment.    It 
may  well  represent  the  basal  deposit  of  a  transgressing  estuary  of  a  large 
bay  like  Chesapeake  Bay,  or  of  a  lagoonal  body  of  water. 
11 


158  THE  PETROGRAPHY  AND  GENESIS  OF  SEDIMENTS 

(2)  The  lack  of  rounding  of  the  sand. 

(3)  The  very  small  proportion  of  heavy  minerals. 

(4)  The  relative  abundance  of  magnetite  and  garnet  in  the  heavy 
portions,  a  character  which  seems  to  be  correlated  with  coarseness  and 
poor  sorting. 

(5)  The  scarcity  of  mica. 

(6)  The  reworked  glauconite. 

(7)  The  freshness  of  the  feldspars. 

This  bed  differs  markedly  from  most  occurrences  of  Matawan  mainly 
in  the  coarseness  of  its  grain,  and  in  the  absence  of  black  clay.  It  occurs 
in  the  following  section  as  recorded  in  the  field,  beginning  at  the  top : 

5.  Monmouth  glauconite  sand  penetrated  by  limonitic  crusts. 

4.  A  marked  £  inch  limonitic  crust  separating  5  from 

3.  A  sandy  transition  zone  (sample  10)  to 

2.  Argillaceous  Matawan  with  finely  disseminated  limonitic  crusts. 

1.  Fresh  argillaceous  Matawan. 

In  the  absence  of  analyses  of  the  underlying  and  overlying  beds  this 
sample  loses  much  of  its  significance,  yet  the  field  relations,  and  general 
knowledge  of  the  two  formations  between  which  it  lies,  in  conjunction  with 
its  own  analysis,  seem  to  point  pretty  clearly  to  its  interpretation.  The 
author  is  then  inclined  to  regard  it  rather  as  a  basal  part  of  the  Monmouth 
reworked  from  the  underlying  Matawan  than  as  upper  Matawan.  The 
general  coarseness  of  the  material  (which  is  of  the  character  of  a  basal 
bed),  the  reworked  condition  of  the  glauconite,  and  the  weathered  condi- 
tion of  the  upper  part  of  the  Matawan,  as  shown  by  the  limonite  crusts  in 
bed  2,  support  this  view.  The  distinction  is  rather  essential.  If  the  bed 
belonged  to  the  Matawan  it  would  represent  a  gradual  shallowing,  form- 
ing a  transition  to  the  coarser  sediments  of  the  Monmouth.  By  the  other 
interpretation  there  was  an  interval  after  Matawan  time  during  which 
the  upper  part  of  the  Matawan  was  weathered,  then  a  transgression  of  the 
Monmouth  which  accumulated  a  basal  layer  of  coarse  material  and 
reworked  glauconite  before  the  typical  Monmouth  conditions  with  the 
formation  of  primary  glauconite  were  reached. 


MARYLAND  GEOLOGICAL  SURVEY  159 

SAMPLE  NO.  11    (FIG.  K,  p.  169) 
Serial  number  :   18. 
Field  number  :  5-10-28-1911. 
Formation  :  Monmouth. 

Locality  :  Seat  Pleasant,  Prince  George's  County,  east  of  D.  C.  Line. 
Appearance  :  A  fairly  light  gray-black,   fine-grained,  very  micaceous,  argillaceous  sand, 
with  many  shells  and  shell  fragments.    This  is  one  of  the  good  fossil  localities  of  the 
Matawan. 

MECHANICAL  ANALYSIS 
Sample    7.185  gm. 

Treated  with  dilute  hydrochloric  acid. 

Per  cent  of 
sample 

Lime-free  residue    94.8 

Lime   (by  difference)    5.2 

Total    100.00 

Per  cent  of 
lime-free  residue 

Sands    80.7 

Clay    18.9 


Total 


Per  cent  of 
total  sands 

Coarse  sand    0.3 

Medium    sand 2.6 

Fine  sand 5.1 

Very  fine  sand 60.9 

Extra  fine  sand    .  .    30.0 


Total 


Per  cent  of 
very  flue  sand 

Light     93.3 

Heavy    6.9 

Total     : 100.2 

MAGNETIC  SEPARATION 

Attracted  at  3000  ohms  (mainly  glauconite) 4.3  1 

Attracted  at  1000  ohms  (mainly  glauconite) 36.9  * 

Attracted  at  full  current 13.0 

Non-magnetic 28.7  2 

Magnetite 17.4  * 

Total    100.3 

DESCRIPTION  OF  PRODUCTS 

A.  UNDER  THE  HAND  LENS 

/.  Coarse  Sand 

(a)  Three  grains  subangular  to  very  well  rounded,  frosted. 

(b)  Four  grains  likewise  rounded  but  glossy  and  slightly  pitted  as  though  corroded  by 
solution. 

(c)  Four  grains  rough,  pitted,  angular,  corroded,  with  much  greenish-black  clay  in 
the  irregularities  of  the  surfaces.     This  shows  a  transition  from   (b),  suggesting  that 
most  of  the  grains  were  originally  rounded,     (a),  (b)  and  (c)  are  of  glassy  quartz. 

(d)  Sugary  quartz,  rough,  fissured,  pitted  and  filled  with  green  glauconAtic  and  black 
clay  stain.    Four  grains. 

1  Glauconite  (see  microscopic  study  below)  may  be  taken  about  37.5%  of  heavy  =  2.5% 
of  very  fine. 

2  Mainly  carbonaceous  matter. 

8  Note  the  unusually  high  magnetite. 


160  THE  PETROGRAPHY  AND  GENESIS  OF  SEDIMENTS 


(e)  Three  very  dark  grains  apparently  filled  with  black  clay  and  green  glauconltc 
stain.  These  are  like  the  grains  In  sample  13  which  are  believed  to  be  secondary  quartz. 
Under  the  microscope  these  grains  show  homogeneous  polarization  and  much  of  the 
included  matter  appears  to  be  mica. 

//.  Medium  Sand 
Mainly  like  the  coarse  with  the  following  differences : 

(a)  The  smaller  grains  instead  of  being  rounded,  are  sharp,  fresh,  angular,  evidently 
primarily  so.     Rounded  grains  are,  however,  still  very  abundant. 

(b)  Dark  minerals  (mainly  magnetite  and  mica)  begin  to  appear. 

(c)  There  are  more  of  the  stained  quartz  grains. 

///.  Fine  Sand 
Characterized : 

(a)  By  the  appearance  of  rather  abundant,  rounded,  yellow-green  glauconite  grains. 

(b)  By  the  angularity  of  the  quartz. 

(c)  By  the  freshness  of  the  quartz,  i.  e.,  little  stained  sugary  quartz  and  no  secondary 
grains  with  clay  inclusions  were  observed. 

(d)  By  the  abundance  of  carbonaceous  fragments. 

(e)  By  the  fact  that  there  appears  to  be  little,  if  any,  increase  in  the  proportion  of 
dark  minerals,  except  glauconite. 

B.  UNDER  THE  MICROSCOPE 
/.  Very  Fine  Sand 

(1)  Light 
Greenish-gray  with  much  mica. 

Quartz  :  feldspar =95  :  5. 

No  distinct  secondary  quartz  or  feldspar  with  black  clay  inclusions,  though  black  clay 
has  penetrated  into  the  fissures  of  a  few  grains,  especially  of  feldspar.  Glauconite 
staining  occurs  but  is  not  abundant.  There  is  no  limonitlc  staining.  There  are  here, 
as  in  sample  4,  some  of  the  rounded,  clay-like  grains  showing  a  faint  aggregate  polariza- 
tion, apparently  transition  forms  to  glauconite.  Glauconite  in  rounded  grains  mostly 
full  of  round  black  granules. 

(2)  Heavy 
The  heavy  minerals  are  : 

Glauconite,  chlorite,  muscovite,  epidote,  tourmaline,  garnet,  amphibole  (colorless), 
staurolite,  zoisite,  rutile,  serpentine,  enstatite,  zircon,  kyanlte. 

The  glauconite  is  full  of  black  granules.  The  chlorite  and  muscovite  are  in  the  same 
condition. 

//.  Extra  Fine  Sand 

Dark-gray  with  many  minute  flakes  of  mica. 

There  is  a  striking  variation  in  the  size  of  the  materials.  There  are  many  small 
opaque  spherical  grains,  showing  a  broken  yellow  surface  by  reflected  light,  sometimes 
agglomerated  into  small  groups.  They  are  doubtless  pyrite  or  marcaslte. 

///.  Clay 

Much  short  fibrous  matter.  Black  spherules  as  in  the  extra  fine-grained  portion,  prob- 
ably iron  sulphide.  Flakes  of  mica. 

Summary  and  Conclusions. — The  mechanical  composition  of  this  sample 
calls  for  little  special  comment.  Its  diagram  shows  the  moderate  sorting 
and  the  abrupt  rise  of  the  curve  on  the  left  with  much  slower  drop  to  the 
right,  which  has  been  shown  to  be  characteristic  of  stream  deposits  in 


MARYLAND  GEOLOGICAL  SURVEY  161 

small  bodies  of  water.  This  would  be  the  conclusion  even  if  there  were 
not  such  startling,  almost  complete  resemblance  between  the  diagram  of 
this  sediment  (H,  p.  169)  and  that  of  the  delta  in  the  Lagoon  of  Thau 
(I,  p.  170).  The  conditions  I  think  may  have  been  exactly  those  repre- 
sented now  by  one  of  the  submerged  stream  mouths  forming  the  estuaries 
of  Chesapeake  Bay,  or  perhaps  by  the  nearer  shore  portions  of  the  main 
body  of  the  bay  near  the  point  of  discharge  of  some  stream. 

The  abundance  of  fossils  encountered  here  for  the  first  time  in  the 
sediments  analyzed  conforms  to  such  an  assumption.  Their  good  preser- 
vation leaves  little  doubt  that  they  did  live  in  place  and  were  not  trans- 
ported. 

The  abundance  of  fossils  encountered  here  for  the  first  time  in  the 
this  type  as  in  sample  4. 

A  peculiar  feature  is  the  low  percentage  of  heavy  minerals  (about 
4.5% ).  But  inspection  of  Thoulet's  analyses  from  the  Gulf  of  Lyon  shows 
that  this  is  so  variable  a  feature  that  it  must  be  largely  dependent  on  the 
original  composition  of  the  material  supplied. 

The  field  relations  of  this  bed  require  some  special  mention.  The  bed 
lies  directly  on  a  white  Potomac  clay,  with  a  somewhat  irregular  surface 
of  contact  but  without  any  evidence  of  a  coarser  basal  portion.  This  seems 
to  confirm  the  above  interpretation.  For  any  swiftly  moving  water 
with  strong  transporting  power,  or  any  body  of  water  with  strong  wave 
action,  must  in  its  progress  over  a  land  surface  leave  a  deposit  of  sorted 
coarse  material,  if  such  is  available.  Now,  such  material  is  available  in 
the  Potomac  bed  under  consideration,  so  that  if  there  had  been  strongly 
agitated  water  this  coarse  material  must  have  been  selected  and  deposited 
while  the  finer  material  was  carried  into  more  quiet  water.  Then  as  sub- 
mergence progressed,  finer  material  would  come  to  overly  the  coarser  with 
a  gradual  transition.  But  if  a  relatively  quiet  body  of  water,  deriving 
its  material  laterally  from  some  nearby  stream  emptying  into  it,  trans- 
gressed over  a  surface  of  such  white  clay,  it  would,  it  seems  to  me,  have 
only  finer  material  to  deposit  and  therefore  put  such  material  down  as  a 
bottom  layer.  Even  here,  however,  slight  wave  action  and  therefore  slight 
sorting  might  be  expected,  unless  the  shore  were  lined  with  water  plants 


162  THE  PETROGRAPHY  AND  GENESIS  OF  SEDIMENTS 

which  broke  up  the  action  of  the  water.  The  lowest  part  of  the  bed  might 
therefore  be  found  slightly  coarser  on  analysis,  but  no  such  difference 
was  noted  in  the  field. 

It  is  to  be  noted  that  while  this  bed  rests  directly  on  Potomac  there 
must  have  been  a  preceding  Upper  Cretaceous  transition  over  the  region 
(to  have  furnished  the  glauconite  which  in  this  bed  is  reworked),  fol- 
lowed again  by  a  period  of  erosion  which  cut  down  to  the  Potomac  beds. 

Minor  features  to  be  especially  noted  in  this  sample  are: 

(1)  The  well-rounded  grains  of  quartz  in  the  coarser  sizes. 

(2)  The  strongly  marked  solution  surface  on  most  of  the  coarser 
grains. 

(3)  The  secondary  quartz  grains. 

(4)  The  grains  representing  a  transition  stage  between  clay  and  glau- 
conite. 

(5)  The  abundant  black  mineral  granules  in  the  glauconite  and  in  the 

SAMPLE  NO.   12    (FIG.  L,  p.  169) 
Serial  number  :  3. 
Field  number  :  11-9-28-1911. 
Formation.  :  Monmouth. 
Locality  :  Sassafras  River. 
Appearance  :  Loose,  coarse,  gravelly,  dark  greenish-brown  sand  with  crumbly  lumps  of 

sand   in   a  matrix   of  grayish-white  clay.     The   loose   sand  appears   to  be   mainly 

rounded  grains  of  yellow-stained  quartz. 

MECHANICAL  ANALYSIS 

Sample 9.235  grn. 

P-er  cent  of 
sample 

Fine  gravel 4.2 

Sand    71.1 

Clay    25.2 

Total     100.5 

Per  cent  of 
total  samls 

Coarse  sand 25.2 

Medium  sand 49.4 

Fine  sand   16.2 

Very  fine  sand 6.0 

Extra  fine  sand 3.0 

Total    "9978 

Per  cent  of 
very  fine  sand 

Light    14.0 

w          f  Rejected  at  2000  ohms 1.8 

eavy^ Attracted  at  2000  ohms   (glauconite) 74.5 

Total     ~90.3  » 

*It  was  at  first  not  Intended  to  weigh  the  products  of  this  separation.  Thus  they 
were  not  weighed  till  after  microscopic  study  when  some  had  been  lost.  They  are 
given  to  show  the  great  dominance  of  glauconite  (the  portion  attracted  at  2000  ohms). 


MARYLAND  GEOLOGICAL  SURVEY  163 


DESCRIPTION  OF  PRODUCTS 

A.  UNDER  THE  HAND  LENS 

/.  Fine  Gravel 

Some  of  the  22  grains  are  quite  well  rounded,  others  very  angular,  but  even  the 
angular  ones  show  a  glossy  surface  that  suggests  solution.  They  are  all  deeply  stained 
with  yellow  ocher. 

//.  Coarse  Sand 

The  glauconite  is  abundant  in  this  portion,  showing  its  original  botryoidal  form,  but 
almost  all  but  the  smallest  grains  appear  more  or  less  completely  ocherized.  The  quartz 
grains  are  like  those  in  the  gravel.  Of  special  significance  is  a  grain  half  feldspar, 
half  quartz  indicating  origin  from  a  nearby  granitic  rock.  The  proportion  of  rounded 
grains  is  less  than  in  the  gravel. 

///.  Medium  Sand 
Differs  from  the  preceding  in  that  more  of  the  glauconite  is  worn. 

IV.  Fine  Sand 
Contains  some  mica  but  apparently  not  yet  any  heavy  minerals. 

V.  Very  Fine  Sand 
A  general  dark-green  appearance  with  dark  limonitic  grains. 

VI.  Extra  Fine  Sand 
The  dark-brown  limonitic  color  predominates  in  this. 

VII.  Clay 
Yellow,  limonitic. 

B.  UNDER  THE  MICROSCOPE 

/.  Very  Fine  Sand 

(1)  Light 
Quartz  :  feldspar  =  75  :  25. 

Though  most  of  the  feldspars,  like  the  quartz  grains,  are  stained  by  ocher,  the  large 
proportion  of  fresh,  unweathered  feldspars  is  striking. 

(2)  Heavy 

(a)  Attracted  at  2000  Ohms 

Almost  all  glauconite,  so  that  the  identification  of  other  minerals  is  difficult.  The 
following  were  recognized:  muscovite,  epidote,  serpentine,  staurolite  (?).  Most  of  the 
glauconite  is  quite  opaque,  at  best  only  cloudily  translucent  at  the  borders. 

(b)    Rejected  at  2000  Ohms 
Dominant. — Muscovite,  enstatite,  zircon. 
Rarer. — Rutile,  garnet,  biotite,  tourmaline,  serpentine,  apatite    (?). 

//.  Extra  Fine 
Many  flakes  of  brown,  granular  ocher. 

///.   Clay 

The  clay  appears  all  granular,  the  usual  fibrous  portions  which  characterize  the  clay 
not  having  been  recognized.  This  probably  means  that  it  is  mostly  secondary  limonitic 
matter,  not  primary  clay. 

Summary  and  Conclusions. —  (1)  It  is  especially  to  be  borne  in  mind 
that  there  is  really  almost  no  clay  present,  the  abundant  material  classi- 
fied under  this  head  being  probably  almost  all  limonite. 


164  THE  PETROGRAPHY  AND  GENESIS  OF  SEDIMENTS 

(2)  The  diagram  offers  little  of  special  interest.    It  is  moderately  well 
sorted  sand,  intermediate  between  lagoon  and  marine  conditions,  but 
nearer  those  of  a  lagoon.    The  usual  absence  in  the  Monmouth  of  the  black 
clay  peculiar  to  the  Matawan  combined  with  this  fairly  good  sorting  sug- 
gests more  open  water  conditions,  that  is,  probably  a  more  general  sub- 
mergence.   The  most  striking  feature  of  the  sediment  is  its  great  coarse- 
ness which,  with  its  regular  bedding  and  uniform  lateral  extension  in  the 
field,  points  to  near-shore  conditions  for  its  formation.    This  leads  to  the 
third  important  feature  to  be  noted,  namely, 

(3)  The  fact  that  in  such  shallow  near-shore  conditions  glauconite  is 
present.    This  is  so  contrary  to  the  usual  assumption  of  quiet  waters  for 
the  formation  of  glauconite  that  one  is  inclined  to  believe  that  the  glau- 
conite is  reworked  from  adjacent  shore  bluffs,  but  in  that  case  evidence 
of  wearing  of  the  glauconite  grains  would  be  expected.    Still  the  author 
does  not  believe  that  any  modern  glauconite-bearing  sediment  as  coarse 
and  as  free  from  clay  as  this  has  been  found. 

Another  possibility  which  suggests  itself  is  that  the  sediment  was 
formed  in  deeper  water  but  swept  by  a  strong  current.  While  there  are 
no  data  for  the  transporting  power  of  currents  in  open  water  it  is  doubt- 
ful that  so  much  of  the  "  coarse "  sand  could  be  transported  by  such 
means.  Moreover,  the  regularity  of  bedding  in  the  field  is  against  that 
assumption. 

It  is  a  peculiar  sediment  and  all  the  more  interesting,  not  only  for  its 
peculiarities,  but  also  because  in  its  general  appearance  in  the  field  it  is 
so  typical  of  the  Monmouth  formation  of  the  Chesapeake  Bay  region. 

(4)  Finally,  an  important  feature  is  the  high  percentage  of  feldspars 
and  their  appearance  of  freshness.     Their  freshness  opposes  the  belief 
that  the  material  is  reworked  from  an  older  sediment,  while  their  high 
proportion,  as  well  as  the  grain  of  combined  quartz  and  feldspar  noted  in 
the  description  of  the  coarse  sand,  point  to  origin  from  nearby.1 

JFor  the  percentage  of  feldspar  in  different  deposits  see  Mackie,  Wm. 
The  sands  and  sandstones  of  E.  Moray,  Trans.  Geol.  Soc.  Edinburgh,  1896,  vol. 
7,  p.  149. 


MARYLAND  GEOLOGICAL  SURVEY  165 

SAMPLE  NO.  13    (FIG.  M,  p.  169) 
Serial  number  :  1. 
Field  number  :  1-9-14-1911. 
Formation  :  Rancocas   (?). 
Locality  :  South  of  Middletown,  Delaware. 

Appearance  :  Coarse  loose  sand  in  a  weak  black  clay  matrix ;  weathering  shows  it  to 
be  full  of  marcasite. 

MECHANICAL  ANALYSIS 
Sample    9.257  gm. 

Per  cent  of 
sample 

Sands »    76.8 

Clay    22.0 

Total    98.8 

Per  cent  of 
total  sands 

Coarse  sand    9.5 

Medium  sand    60.3 

Fine  sand    18.1 

Very  fine  sand    6.9 

Extra  fine  sand 


Total    

100  0 

Light    

Per  cent  of 
very  fine  sand 
.    .    .  .                                                91  4 

Heavy    . 

.      5.1 

Total 


DESCRIPTION  OF  PRODUCTS 

A.  UNDER  THE  HAND  LENS 

/.   Coarse  Sand 

Grayish-white.  Almost  all  grains  are  colored  by  black  clay  occurring  in  the 
irregularities  of  the  surface.  The  solution  effect  on  these  grains  is  evidently  so  strong 
that  it  almost  obscures  the  original  form,  producing  a  glossy  but  very  irregular,  deeply- 
pitted  surface.  Most  of  the  grains  are  of  clear  quartz  but  a  few  are  granular  in  appear- 
ance and  stained  dark  grayish-black.  A  very  few  show  dirty  greenish  staining.  In 
spite  of  solution  effects  it  is  evident  that  the  majority  of  the  grains  were  originally 
rounded  though  there  are  some  that  as  clearly  indicate  an  original  angular  form. 

II.  Medium  Sand 

Much  like  the  coarse  sand  but  with  fewer  rounded  grains,  few  of  the  dark-gray  granular 
grains  and  with  some  heavy  minerals  (garnet,  rutile  ?,  a  black,  very  glossy  mineral  not 
magnetite),  etc.  A  little  marcasite  in  the  cleavage  of  some  grains  but  no  marcasite 
nodules  were  found. 

777.  Fine  Sand 

Like  the  medium  sand  but  with  more  heavy  minerals  (rutile  especially  conspicuous) 
and  the  grains  still  more  generally  angular/ 

B.  UNDER  THE  MICROSCOPE 

7.  Very  Fine  Sand 

(1)    Light 

Quartz  :  feldspar  =  95  :  5. 

Feldspar  much  decayed.  Of  special  interest  are  the  dark-gray  grains  of  quartz,  which 
appear  to  be  full  of  black  flakes  like  the  argillaceous  matter  which  forms  the  matrix  of 
the  bed ;  these  quartz  grains  polarize  as  units.  When  they  are  crushed  the  fragments 

1  By  summation  of  parts. 


166  THE  PETROGRAPHY  AND  GENESIS  OF  SEDIMENTS 


are  found  still  to  contain  the  black  flakes  which  proves  that  the  black  material  Is  really 
on  the  inside.  Grains  of  the  same  kind  were  picked  out  of  the  medium-grained  sands 
(the  dark -gray  grains  mentioned  In  the  hand-lens  description).  Some  of  these  were 
composed  of  colorless  quartz,  others  showed  a  humus-brown  color  throughout  They 
also  polarized  as  units  and  on  crushing  showed  the  same  dissemination  of  the  black 
flakes  throughout  the  original  grain.  I  have,  therefore,  concluded  that  these  grains  are 
secondary,  that  is,  formed  after  the  deposition  of  the  bed. 


(2)   Heavy 
portion  appeared  to  be  magnetite,  and  red  garnet  is  very  common. 

ourmaline,    pyroxene,    chlorite,    enstatlte,    zircon,    silllmanite    (?). 
nd  epldote  are  well  rounded. 

//.  Extra  Fine 

sh-gray,  fine-grained,  very  slightly  micaceous  powder.    This  material 
of  the  samples  because  it  contains  much  that  usually  goes  into  the 


Almost  half  of  thl 
Rutile  is  also  commo 

Rarer. — Epidote, 
Some  of  the  garnet 

A  very  dark,  brow 
is  finer  than  in  mos 
silt.  Under  the  microscope  it  shows  much  argillaceous  matter  in  brown  floccules. 

Many  small,  irregular  roundish  to  perfectly  spherical  nodules  of  marcasite.  Some  of 
the  black  nodules  of  marcasite  are  fringed  by  a  brown,  translucent,  Isotropic  substance. 
In  other  cases  they  are  made  up  of  an  agglomeration  of  tiny  spherules  in  a  matrix  of 
such  substance.  There  are  some  chloritic,  perhaps  a  few  glauconitic  fragments ;  in 
addition  of  course  many  quartz  and  feldspar  grains. 

///.  Clay 

Dirty  brownish-gray.  It  contains  much  of  the  dirty,  fibrous,  polarizing  material  besides 
the  usual  amorphous  brown  flocculent  matter,  and  some  mineral  grains. 

Summary  and  Conclusions. — This  is  a  very  peculiar  and  distinct  sedi- 
ment and  must  be  the  product  of  special  conditions  which  are  only  partly 
brought  out  by  the  above  study,  so  that  no  attempt  will  be  made  to  do 
more  than  indicate  some  of  the  factors  in  its  origin.  The  peculiar  impres- 
sion it  makes  is  probably  due  mainly  to  its  coarseness,  its  truly  black 
color,  its  very  friable  condition,  due  perhaps  to  the  fact  that  the  black 
"  clay  "  binder  (it  is  not  abundant  enough  to  form  a  matrix)  is  not  true 
clay,  i.  e.,  not  colloidal,  or  else  that  the  peculiar  conditions  under  which 
it  was  deposited  destroyed  its  coherence.  The  abundance  of  sulphide 
(presumably  marcasite)  and  coarse  brackish-water  features  of  the  fauna 
sustain  the  impression  of  something  unusual.  One  would  say  a  very  stag- 
nant lagoon,  estuary  or  delta,  yet  the  diagram  (M,  p.  169)  does  not  bear 
this  out,  for  it  suggests  good  sorting,  quite  as  good,  excepting  for  the  clay, 
as  in  the  open-water  marly  Monmouth  (sample  11,  K,  p.  169) .  But  in  con- 
sidering the  sizes  involved  it  is  noticed  that  there  is  in  all  the  diagrams 
presented  not  another  one  (even  marine  beach  sand)  which  has  the  maxi- 
mum in  a  portion  so  coarse  as  the  medium  sand  (1-|  mm.)  It  might  be 


MARYLAND  GEOLOGICAL  SURVEY  167 

that  a  swift  stream  could  deposit  in  its  delta  a  sediment  with  so  much 
coarse  material,  but  the  type  of  diagram  is  too  far  from  that  of  a  delta  to 
make  such  a  belief  tenable. 

Before  attempting  to  adjust  these  facts  some  of  the  peculiarities 
observed  under  the  microscope  should  be  considered.  Foremost  among 
these  are  the  grains  of  what  are  called  secondary  quartz.  Humus  waters 
are  known  to  have  a  strong  solvent  action  on  silicates  and  on  silica.  The 
brown,  humus  coloring  of  some  of  the  grains  of  secondary  quartz  and  the 
envelopes  of  the  same  color  surrounding  some  of  the  marcasite  spherules 
suggest  the  presence  of  such  matter;  yet  no  carbonaceous  ma.tter  was 
found  in  the  bed.  Moreover,  while  decaying  animal  matter  might  have 
precipitated  the  marcasite,  the  apparently  disseminated  occurrence  of 
these  spherules  and  the  fact  that  in  the  field  they  were  not  seen  to  be  con- 
centrated about  the  fossils  seem  to  demand  some  other  agent.  The 
assumption  of  alga?  would  meet  these  conditions  and  be  in  harmony  with 
the  general  stagnant-water  character  of  the  bed.  If,  however,  the  pre- 
cipitation of  iron  disulphide  is  attributed  to  the  animal  matter  the 
secondary  quartz  might  be  accounted  for  by  the  former  existence  of  a 
swamp  overlying  these  beds  from  which  descending  humus  waters  could 
have  produced  the  secondary  quartz,  but  the  knowledge  of  these  processes 
is  still  too  imperfect  to  permit  of  a  very  trustworthy  explanation. 

While  the  assumption  of  origin  in  place  of  the  quartz  grains  described 
seems  to  be  demanded  by  their  internal  structure  it  should  be  noted  that 
this  interpretation  meets  with  a  serious  difficulty,  that  is,  the  outer 
form  of  the  grains.  This  form  is  that  of  the  normal  quartz  grains  in  the 
deposit,  in  part  rather  rounded,  in  part  angular.  If  they  formed  in  the 
midst  of  the  bed  it  does  not  seem  as  though  they  could  have  found  the 
space  to  grow  freely;  they  should  rather  have  involved  adjacent  grains, 
and  the  ends  of  the  other  grains  so  involved  should  give  the  secondary 
grain  a  rough  agglomerated  appearance.  On  the  other  hand,  if  they 
formed  in  some  organic  mold  there  should  be  more  regularity  and  uni- 
formity to  their  shape.  Field  sections  throw  little  light  on  the  problems 
as  there  are  only  a  couple  of  feet  exposed  both  vertically  and  laterally; 
the  only  character  noted  is  the  presence  of  fine  horizontal  clay  films  on 


168  THE  PETROGRAPHY  AND  GENESIS  OF  SEDIMENTS 

which  fossils  are  particularly  abundant,  indicating  fluctuations  in  the 
conditions  of  deposition. 

In  summing  up  it  becomes  necessary  to  neglect  the  diagram  entirely 
and  to  rely  on  the  general  physical  characters.  Here  the  evidence  of  much 
humus,  the  high  sulphide  content,  and  the  peculiarities  of  the  fauna 
are  indications  of  a  very  stagnant,  brackish  body  of  water,  perhaps  sur- 
rounded by  swamps  or  filled  with  disseminated  algal  growths.  The 
region  was  evidently  near  enough  to  some  stream  to  be  affected  by  fluctu- 
ations in  its  transporting  power  resulting  in  the  separation  of  sand  layers 
by  clay  films  and  layers  of  fossils.  But  the  best  explanation  for  the 
peculiarities  of  the  diagram  of  this  sediment  is  in  just  these  secondary 
grains.  It  is  their  development  that  can  account  for  the  coarseness  of  the 
sand,  and  one  may  even  assume  that  they  had  reached  a  certain  average 
size,  between  1  mm.  and  ^  mm.,  to  account  for  the  maximum  in  that  size. 
This  interpretation  is  very  hypothetical,  but  it  is  the  best  combination 
that  presents  itself  for  the  various  partly  conflicting  factors  that  are 
involved.  The  questions  presented  require  more  detailed  and  extensive 
study. 

GENERAL  SUMMARY  AND  CONCLUSIONS 

The  special  features  of  each  sediment  having  been  discussed,  it  remains 
to  sum  up  the  conclusions  arrived  at  and  to  give  a  general  review  of  the 
glauconite  in  the  different  samples. 

CLASSIFICATION  OF  THE  SEDIMENTS 

In  the  discussion  of  the  13  sediments  studied  in  this  paper  three  types 
have  been  differentiated:  (1)  The  delta  type;  (2)  the  estuarine  or 
lagoonal  type;  (3)  the  open- water  glauconitic  type.  The  character  of 
each  may  be  briefly  summarized  as  follows: 

The  delta  type  has  as  its  foremost  characteristic  the  large  proportion 
of  a  wide  range  of  sizes  of  sand  which  a  single  sample  taken  from  it  con- 
tains. In  the  diagram  this  is  expressed  by  a  broad  curve  with  no  pro- 
nounced maximum.  This  character  is  not  very  markedly  affected  by  the 


MAKYLAXD  GEOLOGICAL  SURVEY 


169 


A.— Sample  1.    Magothy 
formation,  Betterton. 


B.— Sample  2.    Magothy 
formation,  Betterton. 


C.— Sample 
Matawan  formation, 
C.  &  D.  Canal. 


G. — Sample  7. 

Matawan  formation 

(calcareous),  Camp  Fox, 

C.  &  D.  Canal. 


H.— Sample  8. 
[Same  as  7  (non- 
calcareous)  .  ] 


I. — Sample  9. 

Matawan  formation, 

Grove  Point. 


J.— Sample  10.     Top  of  Mata- 
wan or  base  of  Monmouth, 
Sassafras  River. 


K.— Sample  11. 

Monmouth  formation, 

Seat  Pleasant. 


L.— Sample  12. 

Monmouth  formatior 

Sassafras  River. 


M.— Sample  13. 
Rancocas  formation, 
near  Middletown,  Del. 


170 


THE  PETROGRAPHY  AND  GENESIS  OF  SEDIMENTS 


A.— Fresh  beach 
sand.     East  In- 
dies.  Mohr,  No. 
213. 


B.— Deeply  weath- 
ered beach  sand. 
East  Indies.    Mohr, 
No.  250. 


C.— Typical  off- 
shore   sediment, 
Gulf  of  Lyon. 
Thoulet. 


D.— Off  Rhone 

Delta.    Thoulet, 

B40. 


I.— Delta  in  lagoon. 
Sudry,  No.  110. 


J. — Dune  sand 
(average).    Udden. 


K.— Dune  at 

mouth  of 
Indus.  Oldham. 


L.— Sahara 

sand. 
Thoulet. 


M.— Stream  allu- 
vium.   Mohr, 
No.  696. 


MARYLAND  GEOLOGICAL  SURVEY  171 

ratio  of  sand  and  clay  in  the  sample,  a  bed  high  in  clay  and  low  in  sand 
containing  almost  as  large  a  proportion  of  coarse  material  in  the  sand  as 
does  a  distinctly  sandy  bed.  With  this  wide  range  in  the  size  of  the  sands 
there  probably  also  goes,  generally,  a  high  ratio  of  heavy  to  light  minerals, 
and  to  a  certain  extent  an  abundance  of  magnetite  (cf.  samples  1-3). 

This  statement  concerning  the  magnetite  is  made  somewhat  doubtfully 
because  there  is  definite  evidence  for  it  only  in  sample  1 ;  it  may  be 
true  also  of  sample  2),  but  there  the  mica  is  so  dominant  as  to  leave 
the  percentage  of  minerals,  more  certainly  classed  as  heavy  by  their 
settling  properties,  relatively  small,  and  it  may  also  have  caused  the 
magnetite  to  be  overlooked.  Abundance  of  magnetite  is,  moreover,  char- 
acteristic of  sample  11,  which  must  be  regarded  as  a  rather  typical 
example  of  the  estuarine  type.  In  the  differentiation,  at  least  of  two  such 
closely  related  types,  therefore,  the  proportion  of  magnetite  must  not  be 
given  much  weight.  A  high  percentage  of  heavy  minerals  in  general 
seems  more  likely,  however,  to  be  a  characteristic  of  the  delta  type. 

A  great  abundance  of  carbonaceous  matter  is  another  characteristic 
of  this  type,  for  which,  however,  the  evidence  given  in  these  analyses  is 
only  qualitative.  With  this  goes  the  formation  of  pyrite,  or  more  prob- 
ably marcasite,  which,  as  will  be  shown  later  in  the  discussion  of  glau- 
conite,  is  an  alternative  product  to  glauconite,  formed  in  the  presence  of 
abundant  organic,  especially  humus  matter.  It  should  be  noted,  how- 
ever, that  as  abundant  humus  matter  is  also  characteristic  of  many 
estuarine  deposits,  so  marcasite  is  found  also  in  these  (samples  11  and 
13).  Furthermore,  since  the  recognition  of  an  opaque  mineral  of  this 
kind  under  the  microscope  is  difficult,  it  is  probable  that  it  has  been  over- 
looked in  some  samples  in  which  it  might  be  found  if  it  were  especially 
sought. 

Finally,  the  form  of  occurrence  in  the  field  is  very  important  for  the 
differentiation  of  this  type,  which  is  characterized  by  thin-bedding,  by 
extreme  difference  in  the  proportion  of  sand  and  clay  in  adjacent  beds,  and 
by  the  occurrence  of  thin  sand  partings  representing,  doubtless,  tempo- 
rary stream  floods.  Moreover,  in  the  argillaceous  beds  the  abundance  of 
mica  is  usually  a  conspicuous  feature  in  the  field,  little  streams  of  carbon- 


172  THE  PETROGRAPHY  AND  GENESIS  OF  SEDIMENTS 

aceous  matter  occur,  and  the  high  percentage  of  magnetite  is  sometimes 
noticeable. 

Under  the  glauconitic-sand  type  only  the  three  samples,  7  and  8 
from  the  Matawan,  and  12  from  the  Monmouth,  will  be  considered. 
Foremost  among  the  characters  of  the  glauconitic  sands  is  their  coarse- 
ness and  the  accompanying  low  percentage  of  clay.  The  figures  for  the 
clay  unfortunately  do  not  bring  this  out  as  clearly  as  they  should,  on 
account  of  the  great  amount  of  ocherous  matter  present,  which  tends  to 
be  separated  with  the  clay.  With  these  striking  characters  goes  better 
sorting  of  the  sands,  that  is,  a  more  sharply  defined  maximum  in  the 
diagram,  and  generally  a  lower  proportion  of  heavy  minerals  (the  glau- 
conite  having  been  deducted  in  these  samples  on  the  assumption  that  it 
was  formed  in  place). 

What  is  called  the  estuarine  type  lies  between  these  two  other  types, 
and  therefore,  naturally,  shows  transitions  to  both  of  them.  Thus, 
sample  5,  the  sandy  yellow  glauconite  bed  in  the  Matawan,  would,  but 
for  its  associations,  be  classed  unhesitatingly  with  the  group  of  glau- 
conite sands.  Indeed,  an  estuary  or  lagoon  from  its  very  nature  can 
readily  become  an  open  body  of  water,  and  there  is  no  reason  why  this  may 
not  be  assumed  to  have  happened  here.  There  is  the  characteristic  sorting 
of  the  sands,  the  only  difference  from  the  other  glauconitic  sands  being 
the  greater  fineness  of  the  maximum  size  ;  but  there  is  no  reason  for  believ- 
ing that  such  a  character  cannot  belong  to  a  typical  glauconite  sand;  and 
the  limited  number  of  analyses  of  typical  glauconite  sands  does  not  justify 
making  a  contrary  generalization. 

The  most  conspicuous  feature  of  what  is  called  the  estuarine  or  lagoonal 
type  is  of  course  the  characteristic  black,  argillaceous  appearance  of  the 
Matawan,  by  which  it  is  so  readily  recognized  in  the  field.  The  cause  of 
this  coloring  is  one  of  the  unsolved  problems  in  the  study  of  these  deposits. 
In  the  normal  samples  of  this  type  the  clay  itself,  when  separated,  is  of  the 
ordinary  blue-gray  color.  The  black  color  cannot  be  attributed  to  organic 
matter  since  that  is,  in  the  most  characteristic  samples,  not  unusually 
abundant,  and  moreover,  it  may  be  seen  from  the  Magothy  that  the  pres- 


MARYLAND  GEOLOGICAL  SURVEY  173 

ence  of  carbonaceous  matter  does  not  tend  to  give  that  color  but  rather 
the  blue-gray.  Perhaps  the  color  is  in  some  way  the  result  of  the  char- 
acteristic on  which  these  beds  have  been  differentiated,  the  mixture  of  an 
abundance  of  fine-grained  sand  with  a  moderate  amount  of  clay,  which 
results  from  the  wide  range  in  the  size  of  the  material  forming  the  bed. 
That  is  to  say,  these  beds  being  predominantly  fine-grained  should  con- 
sist mainly  of  extra-fine  sands  with  much  clay.  But  as  a  matter  of  fact, 
while  most  of  them  are  very  high  in  extra-fine  sands  and  contain  much 
clay,  they  contain,  in  many  cases,  even  more  very  fine  sands,  and  usually 
also  a  considerable  proportion  of  some  of  the  coarser  sizes.  The  most 
marked  exception  to  this  general  wide  range  in  sizes  is  sample  5,  which, 
as  just  stated,  is  really  a  glauconitic  open-water  deposit.  Sample  6,  which 
is  closely  associated  with  sample  5,  shows  much  less  divergence  from  such 
composition;  while  all  the  others  satisfy  reasonably  well  the  description 
just  given.  Sample  9  diverges  from  the  normal  estuarine  type  again 
in  the  other  direction,  that  is,  towards  the  delta  type;  but  its  affinities 
with  this  type  were  already  pointed  out  in  the  summary  and  discussion 
of  it.  To  a  somewhat  less  extent  the  same  is  true  of  sample  11,  as 
was  also  explained  in  the  summary  and  discussion  there.  These  diver- 
gences all  serve  merely  to  bring  out  the  intermediate  character  of  the 
estuarine  type. 

In  conclusion,  if  the  distribution  of  the  three  types  of  sediments  as 
defined  in  the  different  formations  is  considered  it  is  found  that  the 
samples  studied  from  the  Magothy  are  distinctly  of  the  delta  type.  In 
the  Matawan  and  in  the  Monmouth  both  the  estuarine  and  the  open-water 
glauconitic  types  are  found.  This  is  not  surprising.  Even  without  the 
evidence  afforded  by  sample  10  for  the  Monmouth  we  know  and  might 
expect  that  in  both  periods  there  was  transgression,  and  this  transgression 
might  well  be  estuarine  in  its  basal  portion.  Thanks  to  the  good  section 
afforded  by  the  Chesapeake  and  Delaware  Canal,  the  relation  of  samples 
4  to  8  is  clear,  and  it  is  in  conformity  with  this  relation  that  the  higher 
portion  represented  by  samples  7  and  8  should  be  of  a  deeper-water  type 
than  the  lower  portion  (samples  3  to  6).  The  stratigraphic  relation  of 
12 


174  THE  PETROGRAPHY  AND  GENESIS  OF  SEDIMENTS 

the  two  Monmouth  samples  11  and  12  is  not  so  clear,  but  it  is  perfectly 
reasonable  that  sample  11  should  be  of  the  estuarine  and  sample  12  more 
of  the  deeper- water  type  whether  they  are  the  product  of  different  more 
or  less  contemporaenous  facies,  or  of  successive  stages  in  a  transgression. 
There  is  a  general  feature  which  was  not  taken  up  in  the  discussion 
of  the  individual  samples  because  the  facts  were  not  sufficiently  signifi- 
cant. This  is  the  mineral  content  of  the  beds.  It  was  thought  that  some 
light  might  be  thrown  on  the  source  of  the  material  by  the  rarer  minerals : 
but  their  most  striking  characteristics  are  their  similarity  in  different 
beds  and  their  apparently  nearby  origin.  Moreover,  their  resemblances  are 
not  only  with  each  other  but  extend  far  beyond  to  such  sedimentary  beds 
in  general  as  have  been  studied  from  this  point  of  view.  Many  of  the 
same  minerals  will  be  found  to  prevail,  for  instance,  in  the  materials 
studied  by  Cayeux  and  Thoulet,1  or  in  other  such  studies  as  listed  by 
Andree.2  Even  common  experience  teaches  the  prevalence  of  magnetite 
in  stream-borne  sands;  and  epidote  while  less  easily  recognized  is  prob- 
ably almost  as  common,  is  in  fact'  said  by  Van  Hise  3  to  be  one  of  the 
characteristic  minerals  of  sedimentary  rocks.  Equally,  or  even  more 
frequent  are  chlorite  and  muscovite.  Tourmaline,  rutile,  and  zircon 
survive  in  almost  all  sediments  if  there  is  any  source  for  them.  The  per- 
sistance  of  enstatite  in  these  samples  is  apparently  a  more  local  char- 
acter but  can  be  accounted  for  by  the  occurrence  of  the  mineral  in  the 
rocks  of  the  neighboring  Piedmont  region.  It  tends  to  bring  out,  how- 
ever, the  predominance  of  minerals  that  might  at  least  be  of  nearby  origin, 
in  these  sediments.  It  is  this  fact  which  obscures  other  evidence  and  makes 
it  possible  to  say  only  that  the  Piedmont  region  appears  to  be  the  source 
of  most  of  this  material.  But  in  this  connection  two  important  facts 
should  be  noted.  One  is  that  the  Piedmont  region  is  petrographically  so 

Cayeux,  Lucien,  Contribution  a  l'6tude  micrographique  des  terrains  s6di- 

mentaires.  M6m.  de  la  Soc.  G6ol.  du  Nord.,  T.  lv-2. Thoulet,  J.,  Etude 

bathylithologique  des  c6tes  du  Golfe  du  Lion.  Annales.  de  1'Inst.  Oc6anograph. 
T.  iv,  Fasc.  6,  Paris,  1912. 

*Andr6e,  K.,  Sedimentbildung  am  Meeresboden.  Geol.  Rundschau,  vol.  3, 
1912,  pp.  324-338. 

8  Van  Hise,  C.  R.,  A  treatise  on  metamorphism.  Mon.  U.  S.  Geol.  Survey, 
No.  47,  1904. 


MARYLAND  GEOLOGICAL  SURVEY  175 

varied  that  it  could  furnish  almost  any  of  the  more  usual  rock-forming 
minerals ;  the  other  is  a  fact  that  is,  perhaps  on  account  of  its  unwelcome 
character,  all  too  generally  ignored  in  work  of  this  kind,  namely  that 
the  older  sedimentary  rocks — limestones,  shales,  or  sandstones — contain 
heavy  minerals  just  as  do  the  rocks  being  studied,  and  that  a  region  of 
sedimentary  rocks  is  not  going  to  yield,  at  least  at  a  distance,  fragments 
of  limestone  and  shale,  but  rather  the  mineral  grains  that  were  included 
in  the  limestone  and  shale.  Thus  the  problem  is  seen  to  be  a  very  com- 
plicated one,  in  which  only  the  most  general  results  are  readily  obtained. 
If  this  side  of  the  work  is  to  be  developed  it  will  probably  be  necessary 
either  to  find  unusual  minerals  and  trace  them,  or  else  to  differentiate  by  a 
close  mineralogic  study  varieties  of  common  minerals,  such  as  feldspars, 
augites,  hornblendes,  or  even  quartz,  as  Mackie  has  done,1  and  then  trace 
down  to  its  source  the  particular  variety  thus  identified.  This  requires, 
however,  close  study  not  only  of  the  sediments  but  also  of  the  rocks  from 
which  their  minerals  may  have  been  derived,  and  this  becomes  a  long 
and  arduous  problem.  Without  such  work  the  study  of  mineral  grains  in 
sedimentary  rocks  does  not,  in  most  cases,  yield  much  of  value. 

It  will  have  been  noted  that  in  all  the  sediments  studied  the  coarser  sizes 
of  sand  had  a  glossy  pitted  surface  which  seemed  plainly  to  indicate  solu- 
tion of  the  grains  after  deposition.  This  phenomenon  appeared  so  gen- 
eral that  it  cannot  be  connected  with  the  particular  composition  of  the 
bed.  Evidently  the  ordinary  circulating  ground  water  is  the  agent.  The 
chemistry  of  the  process  is  not  understood,  though  humus  waters  are 
supposed  to  be  particularly  effective.  According  to  the  more  recent 
theories,  which  deny  the  existence  of  humus  acids,  this  is  probably  due  to 
the  carbonic  acid. 

More  limited  in  its  observed  occurrence  in  these  samples  is  the  deposi- 
tion within  the  sediment  of  quartz  from  solution.  The  evidence  for  this 
appeared  most  convincing  in  sample  13,  but  associated  with  deposi- 
tion of  silica  there  is  here  to  an  unusually  pronounced  degree  the  same 
solution  of  silica  as  noted  on  the  quartz  grains  in  most  of  the  other 

1  Mackie,  Wm.,  The  sands  and  sandstones  of  E.  Moray.  Trans.  Geol.  Soc. 
Edinb.  vol.  7,  1896,  pp.  148-172. 


176  THE  PETROGRAPHY  AND  GENESIS  OF  SEDIMENTS 

samples.  While  the  coexistence  of  solution  and  deposition  of  the  same 
substance  in  a  bed  seems  at  first  inconsistent  it  may  nevertheless  be 
in  conformity  with  the  recognized  principle  of  chemistry  that  among 
particles  of  substance  in  a  medium  in  which  they  are  partly  soluble  the 
larger  particles  will  tend  to  grow  at  the  expense  of  the  smaller.  Or  the 
nuclei  around  which  deposition  took  place  may  have  been  in  some  way 
chemically  different.  Whether  these  supposed  secondary  grains  have 
definite  nuclei  and  what  these  nuclei  are  was  not  determined,  though  thin 
sections  might  throw  some  light  on  the  question.  The  peculiar  complete- 
ness in  the  form  of  these  grains  was  noted  and  seems  to  be  the  fact  most 
inconsistent  with  the  hypothesis  of  their  secondary  origin.  That  strong 
chemical  action  is  indicated  by  the  abundant  deposition  of  sulphide  in  the 
bed  should  be  borne  in  mind  in  this  connection. 

To  conclude  the  general  summary  it  may  be  said  that  in  all  the  samples, 
no  matter  what  the  form  of  the  coarser  sizes  of  sand,  there  is  never  any 
appreciable  amount  of  rounding  below  the  fine-sand  size  (i.  e.,  ^  mm.  to 
£  mm.). 

THE   GLAUCONITE 

Collet's 1  little  manual  on  marine  sediments  contains  so  complete  and 
up-to-date  a  summary  by  a  specialist  on  glauconite,  contributing  even 
some  hitherto  unpublished  data,  that  it  is  unnecessary  to  enter  into  a 
general  discussion. 

But  perhaps  by  way  of  preface,  since  others  may,  like  the  writer,  have 
considered  glauconite  a  comparatively  rare  mineral,  it  will  be  worth 
while  to  draw  attention  to  its  distribution  in  marine  sediments.  So 
common  is  it,  indeed,  that  Collet  considers  it  necessary  to  explain  its 
absence  rather  than  its  presence.2  It  is  found  more  or  less  along  the 
coast  of  all  the  oceans  at  depths  varying  from  91  m.  along  the  northern 
Atlantic  coast  of  the  United  States  to  3512  m.  in  the  Indian  Ocean.  In 
the  red  clays  which  cover  the  greater  depths,  it  is,  for  some  undetermined 
reason,  absent. 

Collet,  L.  W.,  Les  depots  marins,  pp.  132-194,  303-306.  Paris:  Octave  Doin, 
1908. 

2  Collet,  pp.  303-306,  addenda  on  the  red  clays. 


MARYLAND  GEOLOGICAL  SURVEY  177 

Of  the  three  forms  of  glauconite  differentiated  by  Collet,  all  three  are 
found  in  these  sediments.  The  grains  which  in  this  paper  have  been 
described  as  botryoidal  are  those  called  casts  by  Collet,  that  is,  they  are 
believed  to  owe  their  form  to  their  origin  within  the  shells  of  Foraminifera. 
A  very  few  grains  were  noted  that  had  the  form  of  other  small  shells,  but 
the  shells  were  not  further  determined.  The  description  of  the  products 
shows  that  this  form  of  glauconite  occurs  mainly  in  the  medium  and  fine 
sands,  occurrences  in  the  coarse  sand  having  usually  the  appearance  rather 
of  secondary  agglomerations  of  smaller  grains,  while  only  few  if  any  such 
grains  without  signs  of  wear  are  found  in  the  very  fine  sands.  This  dis- 
tribution means  a  range  of  size  pretty  well  within  the  limits  of  0.3  mm. 
to  0.9  mm.  diameter.  Collet 1  gives  an  upper  limit  of  1  mm. 

The  second  kind  of  grain  defined  by  Collet  is  simply  a  grain  showing  no 
trace  of  an  original  mould.  To  this  category  belong  the  rounded  grains 
which  prevail  in  the  very  fine  and  finer  portions  of  sediments  with 
primary  glauconite,  and  which  as  reworked  glauconite  enter  into  other 
beds.  It  is  generally  agreed  that  they  are  derived  through  the  rounding 
by  attrition  of  the  glauconite  casts. 

To  Collet's  third  type,  the  fragmentary  glauconite,  belongs  what  is 
here  called  glauconite  stain;  that  is,  the  glauconite  adhering  like  clay  to 
the  outside  or  filling  the  fissures  of  mineral  grains. 

Concerning  the  origin  of  glauconite,  Collet's  own  conclusion  that  the 
processes  are  still  very  little  understood  may  be  emphatically  cited.  But 
the  facts  of  observation  at  least  give  much  evidence  as  to  the  conditions 
under  which  it  takes  place. 

It  is  generally  believed  that  a  certain  amount  of  organic  matter  is 
essential  to  the  process,  but  an  excess  of  it  seems,  on  the  other  hand,  to 
interfere.  Collet2  gives  the  formula,  which  appears  to  be  generally 
accepted,  by  which  decomposition  of  organic  matter  precipitates  FeS 
(p.  171).  As  he  explains,  this  FeS  is  believed  to  be  capable  of  giving  up 
its  iron  directly  to  silicates  to  form  iron  silicates,  but  an  excess  of  organic 
matter  interferes  with  the  process  and  thus  leads  to  the  accumulation 

1  Collet,  L.  W.,  Op.  cit,  p.  133. 

2  Collet,  L.  W.,  Op.  cit,  pp.  169,  170. 


178  THE  PETROGRAPHY  AND  GENESIS  OF  SEDIMENTS 

of  pyrite  as  noted  above  in  this  summary.  )Vhether  this  is  due  to  the  pres- 
ence of  an  excess  of  H2S  as  he  mentions  on  page  171,  or  to  the  humus  com- 
pounds (the  existence  of  humic  acids  is  now  generally  discredited)  as  in 
lake  deposits1  has  not  been  proved;  recent  observations  tend  to  show 
that  certain  special  bacteria  are  factors  both  in  the  precipitation  of  FeS 
and  in  its  oxidation  to  FeS,;  but  whatever  the  process  the  fact  may 
be  accepted  that  in  the  presence  of  abundant  organic  matter  in  fairly 
quiet  waters  FeS2  is  formed.  Collet  presents  for  the  steps  of  the  process 
of  glauconite  formation  an  explanation,2  somewhat  simplified  from  that  of 
Murray  and  Eenard,  based  on  elaborate  and  extended  studies  of  his  own. 
In  both  theories,  to  start  with,  a  colloid  is  assumed.  Murray  and  Renard 
conceive  of  the  production  of  colloidal  silica  by  the  action  of  sulphuric 
acid  derived  from  the  oxidation  of  the  FeS  present,  while  Collet  starts 
merely  with  the  colloidal  matter  of  clay.  This,  through  the  processes  of 
sedimentation,  has  naturally  come  to  fill  the  forminiferal  shells  present. 
The  Al  of  the  clay  is  first  exchanged  with  Fe,  and  this  new  compound 
combines  with  potassium  present  in  the  sea  water,  and  also  with  some 
water,  to  form  the  glauconite.  In  support  of  this  theory  Collet  finds 
many  intermediate  stages  from  grains  having  the  appearance  of  fresh 
clay  to  grains  turned  increasingly  deep  brown  by  taking  up  iron.  The 
writer's  observation  of  grains  having  the  form  of  glauconite,  the  appear- 
ance of  clay,  but  an  aggregate  polarization,  was  made  without  any  knowl- 
edge of  Collet's  observations  and  is  therefore  independent  testimony  in 
support  of  this  view. 

The  occurrence  of  similar  material  in  sample  11  (p.  160,  above),  which 
contains  FeS2  (marcasite  ?),  is  perhaps  more  questionable.  Moreover,  on 
reviewing  the  sediments  as  a  whole,  the  writer  is  not  inclined  to  consider 
the  little  clay  accretions  or  nodules  in  the  sulphide-bearing  samples  1  and 
2  as  related  to  the  glauconite.  On  the  contrary,  in  view  of  the  impregna- 
tion of  organic  fragments  with  some  iron  salt  (probably  marcasite)  that  is 
shown  to  have  taken  place  there,  it  seems  more  probable  that  this  same 
mineral  is  responsible  for  the  clay  nodules.  In  fact,  these  questions  can  be 

1  Collet,  L.  W.,  Op.  cit.,  pp.  178,  179. 

2  Collet,  L.  W.,  Op.  cit.,  p.  176. 


MARYLAND  GEOLOGICAL  SURVEY  179 

solved  only  by  getting  different  stages  in  the  processes  involved,  and 
perhaps  by  chemical  analysis,  and  the  present  observations  are  not  con- 
sidered as  sufficiently  extended  to  give  ground  for  interpretation  of  the 
facts  observed. 

In  view  of  the  very  undeveloped  state  of  knowledge  of  the  actions  of 
colloids,  the  uncertainty  about  the  processes  involved  in  the  formation 
of  glauconite  is  very  comprehensible.  The  known  power  of  colloids  to 
absorb  without  chemical  combination  variable  amounts  of  different  sub- 
stances may  also  account  for  the  indefinite  composition  indicated  by 
analysis.  Against  this  apparent  variability  Collefs  protest1  that  most 
of  the  samples  analyzed  were  not  made  up  of  perfect  glauconite  seems 
invalid  since  his  only  criterion  was  fresh  green  color  and,  and  there  is 
no  evidence  that  within  material  of  this  green  color  there  are  not  imper- 
ceptible variations  in  degree  of  what  he  himself  (p.  176)  calls  "  glauconiti- 
zation."  Indeed,  the  wide  difference  in  tone  between  samples  of  glauco- 
nite from  different  localities  would  seem  to  indicate  that  there  is  such  a 
variation.  The  only  analysis  that  could  by  itself  definitely  be  set  up  as 
establishing  the  composition  of  glauconite  would  be  of  good  crystals  of  the 
substance,  but  recognizable  crystals  identified  as  glauconite  are  so  rare  and 
so  small  when  they  do  occur  that  chemical  analysis  has  not  been  possible.2 
Moreover,  it  may  well  be  that  glauconitization  does  not  tend  at  all  toward 
the  formation  of  a  single  definite  compound  and  that  different  glauconites 
are  only  different  members  of  a  series  like  the  chlorites  to  which  they  are 
by  some  supposed  to  belong,  or  like  other  micas.  That  this  is  probable  is 
indicated  by  Collefs  discussion3  of  the  crystal  identified  by  Cayeux, 
which  he  shows  has  different  optical  properties  from  others  that  have 
been  described. 

However,  there  is  strong  evidence  in  favor  of  Collet's  view  of  the 
process.  First  of  all,  it  seems  certain  that  it  must  start  from  clay,  since 
the  foraminiferal  shells  are  sure  to  be  filled  with  that  substance  by  the 
progress  of  sedimentation.  Murray's  assumption  of  sulphuric  acid  to 

1  Collet,  L.  W.,  Op.  cit,  p.  167. 

2  See  discussion  of  determined  crystals  in  Collet. 

3  Collet,  L.  W.,  Op.  cit.,  p.  136. 


180  THE  PETROGRAPHY  AND  GENESIS  OF  SEDIMENTS 

decompose  this  clay,  as  the  initiation  of  the  process,  appears  paradoxical 
since  the  acid  would  first  of  all  dissolve  the  shells  forming  the  mould  and 
thus  allow  the  as  yet  unaltered  clay  at  once  to  disintegrate. 

These  processes,  moreover,  seem  to  account  for  much  of  the  glauconite 
stain,  that  is,  the  glauconite  forming  patches  and  fissure  fillings  on  and  in 
the  grains  of  quartz  and  feldspar  associated  with  glauconite.  It  is,  of 
course,  possible  that  glauconite  is  formed  as  a  fine  powder  from  the  loose 
clay  outside  of  any  enclosing  body,  and  it  may  well  be  this  glauconite 
that  forms  adhering  patches  on  the  outside  of  some  grains.  But  any 
fissure  into  which  this  could  penetrate  would  surely  be  filled  long  before 
by  fine  argillaceous  material,  so  that  here  again  it  seems  that  the  glau- 
conite in  the  fissures  of  quartz  and  feldspar  must  be  formed  by  the  alter- 
ation of  an  argillaceous  product.  The  unusual  thickness  of  some  of  these 
seams  in  grains  of  feldspar,  moreover,  suggests  that  they  are  more  prob- 
ably derived  from  the  alteration  of  kaolin  formed  in  the  fissure  by  the 
alteration  of  the  feldspar  than  from  clay  introduced  from  outside,  since  it 
is  very  improbable  that  an  open  cleavage  crack  of  that  width  would  exist  in 
a  grain  of  feldspar. 

Concerning  the  two  closely  related  problems  of  inclusions  in  glau- 
conite, and  decomposition  of  the  glauconite,  the  present  observations 
afford  only  confirmation  of  recognized  facts.  Thus  the  decomposition  of 
glauconite  to  yield  limonite  is  generally  accepted  and  is  conspicuously 
evident  in  the  open-textured  Monmouth  sands.  The  clouded  appearance 
of  the  grains  of  these  samples  under  the  microscope  is  doubtless  the  result 
of  this  process.  The  occurrence  of  clear,  fresh-looking  grains  in  the 
samples  of  Matawan  from  the  Chesapeake  and  Delaware  Canal  (samples 
3  and  4)  is  on  the  other  hand  probably  due  to  the  protective  action  of  the 
clay  in  which  they  occur. 

Glauconite  with  inclusions  of  black  grains  (pyrite  or  magnetite1) 
were  observed  only  in  samples  8  and  11.  In  sample  8  it  is  note- 
worthy that  the  micas,  too,  are  full  of  black  grains.  Now,  magnetite 

1  The  differentiation  of  pyrite  and  magnetite  from  each  other  when  they  are 
thus  included  in  glauconite  is,  of  course,  difficult  or  impossible  without  chem- 
ical means. 


MARYLAND  GEOLOGICAL  SURVEY  181 

is  a  decomposition  product  of  biotite,  and  biotite  may  also  be  bleached  or 
converted  into  chlorite,  so  that  the  micas  present  in  this  sample  might 
'all  be  derived  from  the  decomposition  of  biotite.  On  the  other  hand, 
this  bed  is  also  sulphide-bearing.  Cayeux  has  suggested  that  pyrite  and 
magnetite  might  be  introduced  into  glauconite  grains  subsequent  to  their 
formation,  but  not,  presumably,  in  a  loose  sediment  of  this  kind.  Collet 
notes  (p.  160)  that  those  inclusions  in  glauconite  are  more  common  in 
ancient  than  in  modern  sediments.  Might  not  these  black  grains,  then, 
be  magnetite  produced  by  decomposition  of  the  glauconite  as  it  is  pro- 
duced in  biotite? 

There  is  one  fact  specially  noteworthy  about  the  glauconite  sands  of  the 
Monmouth,  that  is,  the  coarseness  of  the  accompanying  sand.  The  asso- 
ciations in  the  Matawan  are  normal  since  Thoulet  found  it  even  in  the 
narrow  coastal  strip  of  the  Gulf  of  Lyon  which  he  studied,1  but  its  occur- 
rence in  sediments  as  coarse  as  these  (in  fact  as  the  whole  Monmouth  and 
Eocene  of  this  region)  is  not  recognized  in  modern  sediments.  On  the 
other  hand,  there  is  no  theoretic  reason  against  such  an  association. 

According  to  Collet  the  feldspars  associated  with  glauconite  are  pre- 
dominantly basic,  of  about  the  composition  of  labradorite.  While  no  spe- 
cific identification  of  the  feldspars  present  was  made  the  writer's  observa- 
tions do  not  at  all  confirm  this  conclusion.  The  twinning  characteristic  of 
plagioclase  feldspars  was  exceedingly  rare,  and  the  index  of  refraction  of 
the  feldspars  was,  moreover,  almost  invariably  lower  than  that  of  the 
liquid  (1.548)  in  which  they  were  immersed,  which  would  imply  nothing 
more  basic  than  oligoclase.  These  observations  do  agree,  however,  in  that 
orthoclase  seemed  to  be  scarce. 

The  degree  of  weathering  of  the  feldspars  in  the  glauconitic  samples  is 
very  variable,  and  is  in  these  ancient  sediments  doubtless  determined 
largely  by  secondary  effects  after  their  exposure.  This  belief  is  con- 
firmed by  the  fact  that  feldspars  are  scarcest  in  those  samples  (9  and 
11)  which  show  clearly  their  derivation  from  the  erosion  of  a  deposit 
previously  formed,  which  in  the  interval  before  it  was  reworked  must 

1  Thoulet,  J.,  Etude  bathylithologique  des  c6tes  du  Golfe  du  Lion.  Annales 
de  1'Inst.  Oc6anograph.  T.  iv,  Fasc.  6,  Paris,  1912,  p.  62,  et  seq. 


182  THE  PETROGRAPHY  AND  GENESIS  OF  SEDIMENTS 

have  been  exposed  to  atmospheric  weathering,  and  at  that  time  probably 
lost  a  part  of  its  feldspars  by  decomposition.  Generally  the  feldspars  are 
about  10%  of  the  light  portion.  The  high  percentage  (25%)  in  sample 
10  is  probably  due  to  derivation  of  the  material  from  nearby. 

The  observations  on  mica  also  agree  in  a  general  way  with  Collet's  con- 
clusions in  that  mica  is  not  abundant  in  the  samples  with  primary  glau- 
conite,  while  in  very  micaceous  samples  primary  glauconite  does  not 
occur.  But  this  may  be  due  mainly  to  the  fact  that  the  glauconitic 
sands  are  usually  coarser  and  in  such  coarse  sediments  mica  is  generally 
more  scarce.  More  advanced  decomposition  of  the  mica  in  glauconitic 
samples  was  not  noticed. 


Syroeuf*.  N.  Y. 
Stockton.  Colif. 


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